Half way down in this article you will see various table sizes and room sizes and cue stick lengths and how they all relate.
Home Billiard Room Table Size
Use the info as a guide as to how big a table will fit, with the somewhat "standard" length cue stick, which is BTW, ~57". Then try and fit the largest table that will "fit" n the space, based on the data in the link and go from there.
Most of us believe a good used table is a better buy than some brand new ones. I found my table on Craig's List.
I've also seen a few decent tables offered at Costco, but newer tables haven't been around long enough to have a "history" of performance, durability or stability - so, stuff that's been on the market for only a few years, has insufficient feedback as to price vs. performance. This does NOT make all newer tables suspect, but it lnds to the known history of tables that have been made for years, even decades.
Once you determine what size table will fit, you need to decide two primary considerations. The obvious one being the budget, the second more subtle. Do want a pool table that is first and foremost a pool table?
Or, do you want it to "look nice" as in - "furniture"?
Personally, I find the fancy woods, massive turned legs and gingerbread appliques to be a distraction. Further, the overall quality of the table typically "suffers" - since the manufacturer gets caught between the eye-appeal vs. hidden but critical elements of quality construction, many newer brands are good looking from afar, but play like crap.
Try to not buy a used table that is already disassembled. Obviously it will have to be disassembled to get it to your house... But having a decent pool table technician with you before you pull the trigger would be extremely helpful. It could work like this:
You see the table of your dreams and the price is right. You make the deal with the caveat, "I'll take the table Saturday morning and my tech will disassemble it and bring it to my house and you'll get my cash payment at that time, "PROVIDED MY TECH DOESN'T FIND SOME DAMAGE THAT WOULD RENDER THE TABLE UNSUITABLE FOR MY NEEDS."
How does one find a decent table tech? Anyone you know have a table? Ask them who set it up.
If you play at a billiard hall, ask the owner who does their tables. If you don't play or know someone with a table, go to a nearby billiard (or call them), introduce yourself and ask, "Who takes care of your tables"?
Craig's list is very dynamic. Stuff that was there yesterday will move on - and new stuff comes up every day! If you want a decent used table, check Craig's list daily.