Your lighting and temps sound good, and since you're aware of those two important things, I'm sure you're also aware of the calcium/D3 supplement that should be given to the dragons!
Now, to the rest of the questions:
1) Depends on the sex of the beardies. If they are two females, you could just buy one large tank (I'd say a 180x60x80, at least), and arrange for at least two basking spots, and plenty of room to climb and hide. Although you have to be prepared for the possibility that the two females could not get along, and start fighting. In that case, and in case you have two males or one male and one female, you will need two separate cages once they are a couple of months old. Separating them early is especially important if you have one female and one male, as they could breed at an early age. A female should be adult and healthy before being bred, otherwise there might be serious complications. In other words, get the beardies sexed as soon as possible.
2) & 4) The lighting and temps are just fine, as mentioned above 
3) I assume they're both babies, and in that case they should get as many crickets as they want to eat within a 10 minute periode, twice a day. Remember the calcium/D3 supplement once daily. Also, I hope you're aware of the size-rule: No crickets larger than the space between the beardies' eyes. Larger crickets could kill them.
Good luck!