If he is an efficient feeder, he'll be getting to the hind milk. There's no particular point where fore milk cuts off and hind milk kicks in - but think of it like this, each gulp they swallow is a little fattier/richer than the last. If the baby is really getting too much foremilk there will often be signs like green poops and gassiness. You can certainly offer both breasts, although it's worth noting that if you're worried about too much foremilk, when you swap breasts, he will get another batch of foremilk. Maybe instead you could offer the first breast again after a 10 minute break? That way if he does take some more you will know he is getting richer milk than the first lot he took.
Have you tried skin to skin contact to keep him feeding for longer? Getting him undressed so he is a wee bit chilly can help too, blowing gently on his face, with my LO I found tickling him on his chin helped him to stay away.
You can pump from one breast while he is feeding from the other, or immediately after feeding. It depends what your motivation for pumping is? If you want to increase supply, I would pump from the breast he has just fed from, immediately after he's finished, for 10-15 mins. If you want to get milk to give in a bottle, then I'd probably pump from the other breast at the same time as you're feeding. Either way though will probably up your supply somewhat.
