Turkey flats (body feathers) are handy for parachutes, wings, etc. Take a look at the feather section of any of the online fly tying suppliers and you can see which feathers from the various birds are likely to be useful and what they're useful for. If you're never planning to tie parachute patterns, don't bother with the flats.

A bag of loose feathers would be just fine. Clean them, dry them, fumigate them before mixing with your other supplies.

Turkey biots are HUGE compared to what most folks think of when talking about biots...much easier to get a grip on for tying.

Turkeys also have some cool flat-tipped short feathers that have a stripe of iridescent color on them...there must be a pattern or three that uses that swatch of color effectively (it has roughly the same color characteristics as peacock herl but it's a very different feather compared to herl).