a stock b16a2 block was recently bought with roughly 20,000 km on it,i am putting a rebuilt stock b16 head on and reusing the transmission,i/h/e/vafc with no plans of future modding

new timing belt,head bolts,head gasket,missing anything?
what should i use to clean the pistons?
does my flywheel need to be machined?
should i get the block cleaned/checked/bored before i assemble everything?

 

It would be a great idea to use ARP/new OEM head studs. You will need a new headgasket, timing belt, new water and oil pumps are a good idea while you are at it but you could get away without them if the mileage is really that low. You'll need new intake mani/exhaust mani gaskets. Possibly a new valvecover gasket, depending on the shape of the old one.
You can use sandpaper to clean the pistons if you really must. If it only has 20K on it you shouldn't need to get it honed but you should get the head and deck checked for straightness since it is easy for a shop to check and will save a lot of headaches down the line. You can clean the block with some solvent cleaner and soap and brillo pad and then paint the block so it is shiny and new- to get it hot tanked at a machine shop would require complete dissassembly.
I'm sure I'm missing something here, but that'll covers some of your questions.

 

any new transmission parts that i need?

 

ttt

 

how the hell are we supposed to know?
you can try listing all the parts, bolts, sensors, and wiring that you have... or you can check a service manual. you should already have this in your possession, if you don't go get one.
we can't tell you whether or not you have everything you need... chances are - YOU DON'T