AFAIK, only Kodak and Fuji still make RA-4 paper, and choices in surfaces and contrast are very limited compared to what they used to be. Rumor has it that the Kodak paper handles both Kodak and Fuji films quite well, but that the Fuji paper handles Fuji film better than it handles Kodak film. I can't verify this from personal experience, though. I've not been following it all that closely, but I believe Fuji's been mucking with their papers to make them better for digital machine processing, with the result that new products introduce serious filtration changes for conventional darkroom work. This might be an issue if you only buy a box every few months.
As far as chemistry is concerned, I personally use a mix-it-yourself formula, but there are still a number of commercial ready-made options, including Kodak, Fuji, and a few more hobbyist-oriented kits. The only real "gotcha" I know of is that RA-4 is intended to use the CD-3 developing agent, but one or two hobbyist-oriented kits are built using CD-4 instead. PE has warned that this can result in off colors and reduced longevity, so I'd look into this and be sure that whatever you buy uses CD-3 rather than CD-4. (The agent is probably listed on the MSDS and/or on the box itself.) Some "room temperature" kits exist, but they tend to be more expensive than more conventional products, and the conventional products can be used at room temperature, too, just with extended development time (on the order of 2:30 or 3:00 rather than ~1:00). (FWIW, the mix-it-yourself formula I use specifies both conventional and room-temperature versions; the RT version just adds 5g of potassium hydroxide per liter of working developer. I don't know if this would have the desired effect with a commercial kit, if you should want to reduce the development time.)
