Concentric map worked pretty well for me to play it through on 7ish, without spirecraft or golems on. It was more challenging because I had to hold 2 chokepoints against constantly forming threatballs (cross-planet-waves) and periodic exos, but that was part of the interest of it for me. 1 chokepoint is easier but when you never really have to shift around defensive assets that can make the game less interesting. Still, if getting-it-done is more important, an X map that can fit 5 cities on your quadrant's side of the central world is probably ideal.
A few specific thoughts:
- Unlock mkII and mkIII forcefields, the non-hardened kind (though the hardened ones may be helpful to include), because the spire capital ships and modular city structures get higher-mark shield generators as a result. Though the early capital ships can only use mkII, iirc.
- Similarly, unlock mkII and mkIII laser turrets so your capital ships and cities get stronger versions of their laser cannons, though you may also wish to investigate railcannons (spider turret research) for those light hardpoints. Same deal with the early capital ships not using the mkIII versions, though, so no particular rush on the mkIII unlock.
- There's also mkII through mkIV heavy beam cannons, for the heavy hardpoints. You may also wish to investigate the Plasma Siege Cannons (based off Plasma Siege Starship research) for the heavies (I think only some of the heavies can mount them), but I'm not sure how good they are on defense, and on offense you probably have plenty of firepower with a capital fleet anyway. Same deal on the early capital ships being limited in which marks they can use.
- Remember that the pop-cap provided by the Shipyards is galaxy wide: if you have 1 or 2 cities that actually face attacks, and 3-4 that never see the enemy, you can pile all the shipyards on those "internal" ones and stack the "external" ones with only shard reactors and hab centers. Shipyards have a photon lance too, but they don't get the modules, so the reactors/habs have
way more defensive oomph.
- If possible, have two cities between you and the enemy, so if your outer line is breached you have a secondary defense to fall back on.
- When planting a city that will be handling significant attacks, be sure to place it so that the city shield generators will cover the wormhole that leads into the rest of your territory. With six city structures all mounting shield generators overlapping the wormhole, it can take an enormous attack force to even
think about breaking through.
- During most of the game the city's shields will probably not be enough to hold off enemy firepower, so don't hesitate to pile a ton of normal human forcefield generators on top of the wormhole to provide extra blockage. This will apply the -75% attack modifier to your stuff that is under those forcefields (spire shields do not have that penalty), but if you have your capital fleet on hand and other turrets covered only by the city's shields and not by the forcefields then you should have enough firepower to kill the enemies before they punch through.
- Once you get a galactic capitol you can research the max tier of the shield, laser, HBC, etc modules (if you have the next-lower one already unlocked, of course). The final city shields can be strong enough to hold without help from the human forcefield generators. The highest HBC module is a thing of terror to the enemy. And of course, here you research the BB and DN hulls. Once you have those, the AI won't have much that can stand against you.
As for surviving the final part of the campaign to get the alternate win condition...
stall 
If necessary, glass several planets out from your territory (remember to pick up the knowledge) and put logistics stations on them, just to slow down the enemy. Ambushing enemy forces with engine-damage will effectively take those ships out of the equation. You've only got to hold for about half an hour, so turn on the cheese!
