Let's see if I can help with a few things here:
Add 16x, 32x, and "skip combat" options to make things process as fast as possible. Some turns were a drag with 300+ unit orders to process even at 8x. (At some point there's just so much crap going on that you don't care anymore and just evaluate the state of things after the dust settles)
To skip that, just hit the "end" button when the playback thing is on the screen. Skips the entire playback.
Add "100 dmg" etc. pop ups every time something does damage (disableable)
This one is actually in the Settings menu, under "extras". "Display battle popups", I think is the option, and it will show exact damage numbers with each attack and counterattack.
it seems that events that destroy tiles can destroy icons that have world effects like Yggdrasil and end their effects 
Since I can't smite that tile it kinda sucks that they can be destroyed by random events.
Yep, events that destroy tiles can indeed destroy pretty much anything that you cannot.... this includes tiles that, if destroyed, would cut off a town center from the rest. Important to keep this one in mind... most tiles arent safe when this one occurs!
do guard towers actually do anything or is their effect entirely that AI is dumb and attacks them for no rational reason? Maybe guard towers should make the rest of the town invincible (i.e. must target guard towers first). Or make them give a defensive bonus to units inside.
For the most part, what they do is that normal units cannot cross over or step on enemy towers. They can be used to block off access, basically, and normal units also cannot fire over them. And they have 30,000 HP. The problem though is that beyond a certain difficulty level you'll see alot of units, generally bandits, with the "Bloodlust" ability, which allows them to simply ignore these things. And some types of siege units, Trojan Horses and a similar unit that bandits have, can destroy even these in a single hit with their ability.
how do damage multipliers work? My 2000 damage guy with 1.2x multiplier didn't do exactly 2400 damage to a target.
Well, firstly, make sure that the target is the correct type, or the multiplier carried by the attacking unit simply wont go off. Beyond that though, there's also the terrain to consider, such as forests or marshes or hills, which can have an effect on damage done/recieved by units standing on them, and of course any special effects the units may be carrying. I *think* there might be a couple of small glitches in the damage calculation though, as I've recently noticed a few oddities with it myself, where examining the situation and things like land tiles and buffs simply didn't add up right. I'll see about getting a good example of it caught and submitting that one to the bug tracker.
how does retaliation work? Do both units do their entire hit each time?
Yep.
similarly the degen effects from e.g. Valkyrie are rarely a factor
Yeah, that one I've brought up a few times... I keep thinking their special effects should be changed, same with the Light Elf. For these units, those effects arent the real reason to use them. The Valkyrie is good because of it's incredibly high about of AP; they're stupidly mobile, fairly strong, AND they have a bit of range to their attacks (yet not too much, so they're pretty easy units to manage). Wheras Light Elves often kinda act like mobile turrets, with their massive attack range and multiple shots... they just wont move around all that much, particularly if there's many enemy units anywhere remotely close to them.
I tend to get huge bottlenecks everywhere - could we make friendly units pass through other friendly units (as long as they won't end their turn inside the unit), or maybe make all friendly units stack up to 2 like catapults can, which would go a long way toward helping this.
That one's just part of how the game works... honestly, if you're getting these alot, even with 2 units on one tile, you'd likely STILL be getting them. It's really all up to how the map is shaped, and how you're setting things up, and I think you'll get the hang of it over time. Dont forget that aside from ruins, tunnelled mountains, and bridged lakes, you can always delete tiles with smite, to remove mountains/lakes in the way, as well as place new tiles yourself. These things can be important to keep things moving smoothly. Also pay attention to the TYPE of tile! If you've got a long 1-wide path that has marshes or hills on it, for example, well.... that's just asking for a bottleneck. Yet at the same time, that can be useful for defense....
I was playing on normal (i.e. no veterancy) and at later levels found a lot of high level mythological creatures were around - how is that possible?
Might have been a woe that went off at some point.... I cant think of anything else that can do this.
Gods seem to suck and I've never made one attack or do damage to anything ever. Are we playing the game wrong? They won't go through people or do a path of destruction through people, especially if there's friendlies in the way. I end up dropping their tokens right next to them to get the token effect ASAP.
Originally, they actually DID attack anything that got near them.... and the problem with this was that they killed way, WAY too many things, and could often defend a town pretty much indefinitely. So now, they're passive for the most part.... but they WILL strike back if attacked directly. There's also a particular woe that makes all gods go totally berserk.... they're definitely a threat when THAT one happens! For the most part though, they exist for their passives and tokens.
Why do units ever attack a Cerberus? That seems like a really dumb thing for units to do. We had a game where a lot of Cerberuses got duplicated by Yggdrasil and it basically stalled everything for the rest of the game because everyone would just attack them for no reason instead of pushing to the enemy base etc.
WHY do they do it? Because they're dumber than a sack of hammers
....or because the Cerberus is in the way and they cant get by. Depends on the setup. But yeah, your guys, they're not too good at.... focusing on stuff. They look at an enemy Cerberus, go "OOH A TARGET, BETTER STAB IT", and then probably get all splattered by it's counterattack. That's just how units are in this game, they're not meant to be the brightest bulbs around.
I found that the default 30-turns-per-phase makes for an excessively long game. Maybe the default should be 15 or 20 in order to not scare off first timers? In any case there needs to be a way to make a game shorter than 20 turns per phase for people who like speedier games. Even 20 turns took more hours than we preferred.
This one goes faster once you've had enough time with the game, but in part it can depend on playstyle, or it can depend on how often and how long you are looking at replays. If you're looking at alot of 100+ unit replays with a speed of like x2 or something.... yeah, it's going to add up. Actually spending your actions though can be as fast as you can do them.
We noticed building sorta degenerated into both sides taking turns expanding laterally by building 4 plains as a land bridge and putting a new town there. We ended up having a weird lattice of towns with the rear towns never seeing any action. That was pretty weird. Maybe the # of blocks that comes each turn should increase with the # of towns, and maybe they should perferentially try to connect towns or something.
Sometimes this one can depend a bit on luck; I've had plenty of times where I'll have an intended land bridge, thin and defended by stuff, usually leading to a resource-only town.... that then gets a pile of landtiles appearing next to it ANYWAY, screwing up my plans for defense. But yeah, I agree, the land-expansion rate should increase as the game goes further along. Should go up as ages switch.
Hope some of that helps!
