Just give an idea of a SMALL BOD library - my own.
Tailor BODs:
I keep 1-4 BOD sets on hand of EVERY small BOD that goes to a Barbed Kit, Horned Kit or CBD, separated into books by LBOD type. In the case of Barbed Leather LBODs, I'm more likely to have incomplete sets with an LBOD (or multiples!). I also keep similar sets of spined kit smalls, but don't actively fill them currently (I have 50+ kits on hand). This works out to about 500-700 smalls, in said sets, not counting the 300 or so cloth BODs.
The BODs over and above those in my library, that would fit these, go into books on my vendors - not for storage, but for sale. They rarely sell, even at 2000 or 3000 each, and if I get a large BOD for a good reward, I fill it from the vendors first, if possible.
When I was actively cranking through BODs, I'd fill 100-200 small BODs (mostly normal cloth & leather that I could fill through buying, minimizing resource consumption/costs). I would get about the same number of BODs back, about with about 1 in 5 being one to potentially go into one of my library or vendor books. After throwing away the bone BODs, the rest of the BODs go into the next day's turn-in pile (or, I can just turn around and fill them again). Each 100 BODs will typically have 3-5 Larges for rewards that are keepers (and a few that are absolute junk - it averages out an 8% chance that any given Tailor BOD drop is a large).
Once you get to a BOD collection that size, with about 10-20 new BODs a day (even 0.1 skill ones that only get small normal hat BODs can help you get there, but I use 6 Tailors that are eligible for the full spectrum of BODs), the amount of BODs in your permanent library gets almost self-sustaining, with new BODs replacing the ones used.
So, figure that you can get 3-5 good rewards a day per 100 BODs turned in, as most small BODs pulled from those 3-4 sets per LBOD type will be replaced by the smalls from the BOD cycling.
One of the best sessions I ever had was turning in 200 small BODs, and coming up with the larges for 4 Barbed kits and 7 Horned kits, as well as 4 CBDs, plus the smalls needed to finish 2 other Barbed kit larges I'd been missing the last small for (Barbed leather). I also ended up with another 100+ smalls to fill for new BODs (though 1/3 were exceptional smalls, that I had to craft items to fill, or for things like Bonnets, surcoats, full aprons or body sashes, that aren't for sale).
If you can keep up with the boredom and hand cramps, that base library size can keep you reasonably in runics - and the amount of runics is limited only by the time you wish to put into it (as it takes about 60-90 minutes to fill 100 BODs, and another 30 minutes to turn them in, get replacement BODs, and sort the replacement BODs).
I'll actually give you a diagram of my Tailor BOD collection, to give you an idea of what to shoot for. This is not counting cloth BODs, and most of my "for sale" BODs.
Regular leather
Bone EX x20 = 4 x 5 smalls
Studded EX x20 = 4 x 5 smalls
Male Normal x20 = 4 x 6 smalls
Male EX x10 = 4 x 6 smalls
Male EX x15 = 4 x 6 smalls
Female Normal x20 = 4 x 6 smalls
Female EX x10 = 4 x 6 smalls
Female EX x15 = 4 x 6 smalls
Total: 184 smalls
Spined Leather
Bone EX x10 = 4 x 5 smalls
Bone EX x20 = 4 x 5 smalls
Studded EX x10 = 4 x 5 smalls
Studded EX x20 = 4 x 5 smalls
Male Normal x10 = 4 x 6 smalls
Male Normal x20 = 4 x 6 smalls
Male EX x20 = 4 x 6 smalls*
Female Normal x10 = 4 x 6 smalls
Female Normal x20 = 4 x 6 smalls
Female EX x20 = 4 x 6 smalls*
Total: 224
* These are the easiest 100% Barbed kit sets to get smalls for, as the weird setup for Tailor BODs makes Spined BODs actually more common than normal leather. Having gotten 2 of the same large in 1 100-ish BOD turn-in before, for these, I make sure to keep extras on hand (and even pre-fill some of the components, if my BOD runners can get gains on the parts).
Horned Leather: Here, it becomes hard, for some reason, to get more sets than 2 of the 5-parters. It SHOULDN'T be (every small BOD type is SUPPOSED to be equally common, after material type is selected), but I can get 5 sets of any 6-part horned in the time it takes to get 2 sets of the equivalent 5-parter.
Footwear EX 20: 2 sets of 4 smalls (these are a lot more rarer than one would think - STILL haven't actually managed to get an LBOD to fill)
Bone Normal x20 = 2 x 5 smalls
Bone EX x10 = 2 x 5 smalls
Bone EX x15 = 2 x 5 smalls
Studded Normal x20 = 2 x 5 smalls
Studded EX x10 = 2 x 5 smalls
Studded EX x15 = 2 x 5 smalls
Male Normal x10 = 4 x 6 smalls
Male Normal x15 = 4 x 6 smalls
Male EX x10 = 4 x 6 smalls
Male EX x15 = 4 x 6 smalls
Male EX x20 = 4 x 6 smalls
Female Normal x10 = 4 x 6 smalls
Female Normal x15 = 4 x 6 smalls
Female EX x10 = 4 x 6 smalls
Female EX x15 = 4 x 6 smalls
Female EX x20 = 4 x 6 smalls
Total: 308 smalls
Barbed Leather: Most of these are TARGETS. Barbed smalls are so rare you're hard pressed to ever get 2 sets ready, before the equivalent large falls into your lap - and sometimes have to wait weeks for a small to finish a large you do get...
Footwear EX x10: 1 set x 4 smalls (too hard to even try for more)
Bone Normal x20 = 2 x 5 smalls
Bone EX x10 = 2 x 5 smalls
Bone EX x20 = 2 x 5 smalls
Studded Normal x20 = 2 x 5 smalls
Studded EX x10 = 2 x 5 smalls
Studded EX x20 = 2 x 5 smalls
Male Normal x20 = 2 x 6 smalls
Male EX x10 = 2 x 6 smalls
Male EX x15 = 2 x 6 smalls
Male EX x20 = 2 x 6 smalls
Female Normal x20 = 2 x 6 smalls
Female EX x10 = 2 x 6 smalls
Female EX x15 = 2 x 6 smalls
Female EX x20 = 2 x 6 smalls
Total: 160
Grand total: 716 Normal-Horned, plus a target of an additional 160 Barbed, for a total size of 876.
Build up to something resembling this kind of library, and then spend 3-4 hours a day filling, turning in and claiming 100+ smalls a day, and soon you will be awash in rewards.