I wouldn't worry Imi. BOMs are all about trying new blocks and seeing what you like. You van make multiple of the same, or different fabric variations after you have tried them out. Fitting them all into a quilt is possible, just needs some thought - so repeat a row of the smaller ones, use some sashing to split up areas of similar design etc. Or make table runners, cushions, make lots of quilts out of blocks tested out in a BOM.
BOMs have always been a nice non committed way of trying new designs to see if it suits you. Not a way to get to a sampler quilt. Nothing against sampler quilts, but generally they have recurring fabrics and the blocks are all in a similar style - so a sampler of traditional blocks, of HST blocks, of Amish block, modern blocks, wholecloth pattern blocks, etc etc.
Thes BOM is not to create a sampler or a non sampler quilt, but to allow people to test out their skills on new ideas and on blocks they might never attempt!
If you would like some help on the contribution side I'd be happy to oblige. I've a tonne of inherited books I haven't yet done things from and have no real reason other than a sampler quilt and I never put it at the top. So contributing a block for people every so often would be great. I'd be happy to tackle some complicated ones that you don't like as well! And I need something to push me to make my cathedral mini quilt!
It's a lovely thing you've started. I haven't joined in because I can't find my fabric hamper and I'm eyeball deep in riding habit!