Hi, I've done a fair amount of home recording of anglo/celtic Appalachian Old Time and British Isles/Irish/Scottish, and I find it's mostly a question of mike placement and choice as long as your signal chain is pretty decent.
Both large and small diaphragm condenser studio mikes work well with a number of instruments, and the main concern is a quiet path for the intimacy of the instruments such as fiddles, guitars, banjos, bouzouki, octave mando, mando etc. Small diaphragm condensers work well on tenor banjo. About a foot away from the head, pointing at it, maybe a little off axis. Large or small on fiddle, viola, guitar.
An omni will work well real close up cuz you'll not have the bass proximity effect of a cardioid, which studio condensers tend to be, unless they have a pattern switch. I have it on good authority an Earthworks TC30K is great for this kind of omni work. I don't have one. Also, ribbon mikes, but they generally don't have great output, and so turning up the preamp to compensate can raise the noise floor in an acoustic situation.
I've not recorded pipes.
I'm not a real good bodhran player, but have found that instead of using a tipper, if you hit the drum with the tip of your middle finger, like a doctor asculting a patient's chest, you can get good tonal response, though alot of traditional technique flies out the window at that point.
Absent a stand up bass, I've used a wooden bridged Danelectro bass and it approximates the sound of one, if you need that, unless you want a rock sound(ala Tannahill Weavers on some of their stuff. where you might just grab a Fender Precision or whatever)
In an ensemble recording situation, a stereo mike setup would yield good results, though I've always done mostly my own stuff, and was overdubbing everything. I haven't done that, but know that's an option.
With older types music(medieval, celtic) a big unused stone church will yield great results(I know, I've heard examples,) but they're not that easy to be had, as I guess you know.
Primarily it's a matter of keeping the mike chains with as low a noise floor as possible, especially if alot of overdubbing is done. The more mikes used for takes the more the noise accrues. With dynamic instruments like fiddle and bodhran, an optical limiter in the chain right after the preamp is a great help against digital overs. (assuming you're recording digital,,,they can be a help in general) Good mikes,,good preamps,,a little limiting, and no coloration of EQ in the recording chain should be good. Get the purest sound of the instrument you can. I guess alot of this is self evident,,but I've had a little experience; hoping it's of some help.
If you go to
http://littlebluemen.com/beth.htm and address any email queries to Beth, she could be a goldmine of info. She's more experienced at this than I. You should find an email link if you click on the 'contact' icon.