IMHO a 300 gallon with a couple of canistor filters, I believe the OP stated Fx6's were going to be used (I assume that the tank is not being drilled?) , is not a big deal. The tank is ordered, money has been spent, it may even be in shipping mode at this point, either way there is no turning back. I would have added a sump to the mix, but perhaps that would have been too complicated for the OP, who knows? Not everything has exactly been well thought out thus far.
Everyone is entitled to their opinion here, but I'm not sure how a differing of opinion = MFK goal posts are moving? lol
Hell, i would line up 8 feet worth of ac110s and call it a day! Heater in the least noticeable corner of course.
I think what your boy meant with the goal post analogy was its becoming harder and harder to please the would be powers around here, and easier than ever to offend them. I'll not say more, but instead will observe a moment of silence for the loss of a respected forumite, @Dloks