Welcome to Librarium Online!
My current table is 6x4... I have plans for a new one that will be 8x4 and modular (all home made).
6x4 is what you want for most games... if you're going to go Apoc then you'll want more... or if you play 3-4 person games an 8 ft table might be called for?
Mine will have two 1 ft wide "boxes" that will sit on either end, lined with felt, for reserves/deadbox and dice rolling on a 6x4, remove them for an 8 ft option.
I plan to use a table tennis table - 9x5 foot, I will probably make a 6x4 foot frame to sit on top and use the extra space for casualties/reserves, books, templates dice etc