If I went with 2 subs, does the 2nd sub connect off of the 1st sub?
If your AVR has a single subwoofer output, you just use a Y-splitter to split the signal to both subs.
... do people with dual subs ever stack them or should they always be placed around the room for better effect.
Yes, people do (occasionally? often?) stack their subs. Co-locating / stacking your subs usually provides a few more dBs of SPL vs. separating the subs, while placing the subs apart offers better overall FR at the listening position (LP) vs. co-located subs.
But if you're already getting a good overall FR at the LP, you may find it worthwhile to get the extra dBs from co-location vs. trying to improve on the FR.
My room is 22x14 but it has large archway openings and half wall going to the large Kitchen area which is almost the same size.....with Cathedral ceilings.
If each room is at least 3,000 cu.ft. (22' x 14' x ~10'), that's a lot of volume to pressurize. You should probably be considering duals (right away; or, get one now and add one later on) of more powerful subs instead.