So a female is best, but if you can't find one a male bun is perfectly fine as well, don't worry xxx
I know many people that have same sex bunnies together and it turns out just as great as male + female
I would definitely recommend doing it slow as you do have two males, they won't fall for each other in the same way.
I'm no expert so you should get vet advice as well but i would bond them in a neutral territory, with two close enclosures or a run with a splitter in the middle.
On the very first meeting you should never let them loose as without sniffing each other through bars first, because they will attack :/
Make sure both are suited to each other first
As with the food, yes you should definitely change from muslie to pellets, it is so much better for them. To do this, it's quite simple, you need to add pellets gradually to their food mix over a week or two, until their food has completely changed to pellets. If he throws a tantrum, don't give back the muslie, just coax him into eating the pellets. Of course, you should do this as soon as possible but i'd ask a rabbit expert/vet about whether to do this before or ater the bonding.
Hope this helps x