you really won't need to worry too much about separation, but if you want to have makeshift gobos, use some type of structure and moving blankets. You can get these pretty cheap (i actually stole like 7 of them from Uhaul--they were in the back of a trailer I rented for moving, and I kept them). Old matresses help deaden as well, and you can usually find them at goodwill for like $5. Regardless, it's not crucial.
Upright bass can be tricky to master. If the artist has any sort of electronic pickup, that can make things really easy. I am going to assume the player in your setup does not have one, and that your only option is mic'ing. First off, keep the mics for the upright within about a foot of the sound source. I, for one, don't like too much "room" in a bass track. It can lead to muddy tracks. We can always add reverb or room tone later. Ideally, use a 2 mic setup on an upright. I large diapragm condensor just outside the f-hole would be the first mic, and the second can be either a small diaphragm condensor or another large diaphragm just above the bridge, aimed towards the hole to your liking (try experimenting with different angles until you get the tone you like).
Acoustic guitars can be mic'd SO MANY different ways, but what I have typically has results with is the following:
one condenser about a foot away from the guitar aimed where the neck and body meet and also towards the hole, without being pointed directly at it...I find that micing the hole leads to a very boomy guitar, which while occassionally desireable isn't always the most flattering tone. I also like to put another mic aimed towards the bridge (again, about a foot away). By playing with the mix between these 2 mics, you can achieve a nice sound. If you only end up with one mic on the guitar, go with the first placement (where the neck and body meet).
I have never had the opportunity to mic a fiddle, but I got this from another enigneer, and it makes sense to me:
Violin / Fiddle: recommended Neumann U-87, Neumann KM-184, AKG C-460B
If you want a bluegrass / country fiddle sound with lots of bite, place the mic directly
above the bridge about 8" - 10" away. The smoother the sound desired, the farther away
the mic should be - up to 3 or 4 feet away if necessary and the more off-axis. I won't use
anything but a condenser on violin.
I have also never mic'd a banjo, but from what I hear, a 57 (or a condeser) aimed at the drum head should provide adequate results.
What are you using for vocal mics? How are these positioned?
As I change my mind on mic'ing techniques, I'll re-post...It's really a feel thing. Place a mic, go back to listening position, if you don't like how it sounds, change angle/distance/mic, repeat.
As far as me helping you out...I'd really like to try some things (like fiddle and banjo micing). My only necessities for an overnight stay would be a couch where I can throw a sleeping bag (although a bed would certainly be better). Let me know...it's not that far for me to drive up there...
h