Shawn,
It sounds like you have already done some research, but in case you haven't come across these sites, there is a ton of knowledge to be gleaned and the forums are very "hobbyist friendly".
www.homeshopmachinist.net
www.chaski.org/homemachinist
www.homemodelenginemachinist.com
Unfortunately, if you want a machine larger than what Sherline offers, there are little, if any new high-quality machines available. This leads to the decision of buying the "classic" American iron that may have seen better days vs. the new, but crap-shoot quality of the off-shore machinery. I think smart men can argue the merits of either choice.
If you decide a Bridgeport mill will not fit in your basement and start looking at smaller models, pay attention to the max. spindle to table distance. Some of the models have around 13" -14" inches which sounds like plenty, but when you add a 3" chuck, 3" drill bit and a 3" vise the distance disappears quickly.
Some good mills that are approx. 2/3 the size of a Bridgeport are the vintage Rockwells, Clausings and Millrites. They usually have a 6" x 24" table and most of those can be disassembled to get into tight spaces.
The only other advice I will give is to think long and hard before buying a 3 in 1 machine (lathe, mill, drill press). There are definitely guys that turn out beautiful work on them but having separate machines will make your life a lot easier.
Good luck on your search!
John