Cant help you on the diff capacities, but to fill it you may need a oil suction pump (some of them are rubbish and it seems like its hit and miss with them). Chris can tell you what he did, there should be a thread on it somewhere.
Just fill it until the just starts to come out of the fill plug hole. The drain plugs are at the bottom so no special hoses or suckers to get the oil out. Just remove the drain plugs and let the oil drain out. If memory serves it is between 2.5 and 3 litres for both. For the rear diff you will need a 24mm socket for both the drain +fill plug (try to use a six sided socket cause if the plugs have not been out before they will be hellish tight).
For the front you will need a 10 and 12mm allen key, best the socket type. These are not in a good place to get to but do-able, go careful if you round these out your are on a road to hell.
Start with the fill plugs first as it is better to find out you can't re-fill the diff whilst it is full oil rather than draining the oil then finding out you can't fill again
Just one other thing get some replacement washers for the plugs as they are a none re-usable item, they are only pennys from Mr.T and they usually have them in stock.
Cheers guys. The crush washers are already on order (should hopefully pick them up tomorrow). I will pick up 6 litres of gear oil tomorrow as well - where can I get gear oil in 5 litre containers? Both Toyota and Halfords only seem to have 1L bottles..?
Quite an easy way Tony and I did LB's front one was long piece of tube through the engine bay, tony under it barking orders.
To add to Steve's - you need to fill it till it dribbles out, close the filler gently, drive around a bit and put some more in. Not sure if that is for the front's with lockers such as LB's or for all.