I can't remember the exact cargo capacity off the top of my head, but during a four month period we loaded cargo three times - Loch Striven, Djibouti and Fujairah. On each occasion we loaded about 6,000cz of marine gas oil ("dieso" or "F76"). We would also load around 1,000cz of aviation fuel ("AVCAT" or "F44"). We also did a pump-over with Bayleaf at sea of about 3,000cz, but it was a swap, we gave them our UK-spec cargo and we took their locally sourced cargo. We also had the capability to produce fresh water and could carry about 400cz in cargo fresh water tanks. Exactly how much all that cargo lasts depends on how many RASes we do and how thirsty the warships are. On at least two occasions Illustrious took over 1,000cz of F76, and I can remember one American destroyer (either the Russell or the Cole) taking 600cz. Most RASes however are less than 500cz. We also take our own bunkers from the cargo, Wave Knight's bunker capacity being around 1,400cz.
Exactly how fast we can RAS depends on how competent the XO is (he is the one controlling the cargo operation during the RAS) and how confident he is in his equipment, and of course how fast the receiver can take it. The cargo pumps on Wave Knight can pump at about 600cz/hour, but we very rarely pumped at that rate. I can remember Edinburgh had problems with their pipelines, and the MEO wasn't happy for us to pump over to them at anything more than 50cz/hour, and even then they were very nervous. Then of course the Pakistani frigates in the pics had problems too, and they seemed to be spilling as much dieso into the sea as went into their bunker tanks. Eventually the Chief Engineer on Wave Knight called a stop to the evolution as he wasn't happy with filling the Indian Ocean with our cargo

We can RAS up to three ships at a time, with one on either side and one astern. The MCA really doesn't like the idea of us doing a stern RAS though and the capability is there only if we really need it. I have only ever seen two stern RASes before and they were both dry hook-ups (i.e. just for training, no fuel was pumped). We did attempt to do a stern RAS with Fort Austin with a token 15cz of F76 but it was a complete disaster. The pipework from the cargo pump to the stern RAS rig had been blanked off and we had to put the bobin piece back in, and when the XO fired up the pump the bobin piece leaked very badly and we flooded the compartment with F76. The RAS was abandoned and it was decided not to listen to the XO any more when he has any bright ideas about stern RASes
The Rover Boats obviously have a much smaller capacity, I can't remember off the top of my head but it is smaller than a Wave Boat or Leaf Boat. The Leaf Boats have an enormous cargo capacity but they don't use it as they aren't double hulled. They always sail with the wing tanks empty and carry cargo only in the centre tanks. This still leads to problems as the tanks aren't double bottomed so the Leaf Boats (and Rover Boats now too) aren't welcome in many commercial ports as they don't meet the latest regulations. One of the real advantages of the Wave Boats (other than their speed, big flight deck and flexibility) is they are double hulled and are built to the latest specifications and as such can use any port in the world.
The two best tools in any engineer's inventory are brute force and ignorance and he should always live by the engineer's motto "Bodge it and scarper!"