where to start
first - you are not putting all your eggs in one basket since you are playing with friends. only if they too put all their turrets on the same planet as you we have a (for me) troubling situation
this brings me to my second point - if only your turrets cover the warp point then my previous deduction holds true that is impossible for you to wipe out a wave of mark v and iv ships including bombers and electro shuttles instantly
and finally third - if you dont wipe em out instantly just having forcefields there to contain the ships for your aoe turrets will lead to a very short and painful experience in the area of turning high value installations into scrap metal (but thats just my 2 cents)
anyway just to clarify this for future replies - yes, i think forcefields are necessary for a warp point defence BUT not on their own. some_randoms idea is not bad but ff only will not work (at least for me using 3.172)
and everybody replying was avoiding to say something concerning efficiency - i know that the game is not about micro management but totally ignoring efficient placement of your assets will not make the game easier - but feel free to prove me wrong