As you've asked me specifically in another thread:
Prime at what level?
Well, I think I know you were asking for "cask" levels? About 0.5g per litre, gives about 1.2-1.3 volumes (presuming you ferment beer out before casking?). So, for headspace in half full cask, add another "volume" ... that's about 0.5+0.4g per litre of sugar. Say, 9g sugar in a 19-20L Corny with 10L beer.
BUT!
Get it a bit wrong (or drink about 1/3 without priming again) and you are using some form of manual (hand) pump, (and presuming this is your "no gas cylinder" caper) and the priming sugar gas runs out (it will, leaving atmospheric pressure in the cask), the pump will pull air in past the Corny keg lid seal! And the beer goes off a few days later.
You could add x2 the headspace sugar, but the beer will be (initially at least) very fizzy.
KEG
The usual (per litre) plus same again for headspace. No pump problem ... no gas, no beer comes out tap! Add same again of sugar (x3 what normally added) to ensure right gas at end (but fizzy to start).
Don't use any form of electric pump for dispense.
Have I made you think again? I hope so.