Seedlings in 5 gallon buckets...

I have recieved a large number of bare root oak seedlings. I don't want or need this kind of oak in my yard, but I thought I might pot them up and grow them out to sell or give away.
So should I use 5 gallon buckets, or can I use something smaller to get to them to a sellable state? Can I use my poor clay soil, sifted and top dressed with compost or will this stunt the growth? Should I maybe plant annual legumes or a mimosa seedling in the same pot?
Should I make sure they can drain completely or leave a reservoir ?

Obviously drainage will be important, so drill some 1" holes around the base of the buckets. A paddle bit on a cordless drill will make quick work of it.

Straight clay isn't the best soil for a potting mix, so can you amend it a bit with organic material, perlite, bio char, etc? Oak roots will drill down, so that won't be a problem -- they send down a strong tap root, but a bit of amending of the soil will help with drainage and help the tree get a better start.

I've used lots of buckets as pots, with random local soil (commercial potting soil isn't available within thousands of miles from where I am). I don't always have success but I certainly don't know if that's my soil, or my occasional watering lapses in this intensely hot dry sun, or what.

I use a hot nail to make lots of small holes so not too much soil comes out. It makes perfect little round holes. A collar of melted plastic rises on up on the side you push from, so it makes a smoother finish if you push the hot nail from the inside of the bucket. I balance two long nails or spikes on the gas burner with all the windows and doors open and a good cross breeze, and try to hold my breath to avoid the plastic fumes. It doesn't seem very safe, fume-wise, I'll admit.