In ur opinion dule 400 wouldn't be overkill in my 2x5 tub...im putting ply wood down so its more of a rectangle n gives more floor space..im deff looking at cool tubes and a carbon filter
yes, 800 in there could be overkill if not properly ventilated. but i have been on your shoes, so let me share.
if you do cool tubes or air cooled hoods, you can easily vent that all into the existing ceiling fan, making things super easy. as long as it is properly sealed, all you are doing is exhausting air that the lights made hot. nothing stinky gets sent into the neighborhood.
for the rest of it, here is what i would suggest: you need to use a carbon filter if smell is an issue, and you need a somewhat expensive fan that can move at least 250cfm through that carbon filter and out the window. although my bathroom did not have a window and i had to vent elsewhere, there is a good trick for venting out of a window without raising any suspicion. the idea is to get an old window AC unit, working or not, and install it such that the facade that others can see looks like an AC unit but is actually just a way for you to exhaust your carbon filter air.
intake fan is optional if you have a good exhaust system in place, but i would suggest something small like a PC fan or two.
if you have good ventilation, you can do 400s, but 250s will suffice and make life easier. and you are probably better off doing 10-12 SOG plants in that type of space rather than doing 35-40 lollipopped ones.
best of luck.