Raised vegetable bed questions
I'm both new to Arizona and gardening at the same time. I picked up some 2x8's to build a 4'x10' box which I was originally going to set into the ground but now I believe I want to go with a raised bed. I wish I would have bought 2x10's or even 12's but I can replace or add on later if needed. I've decided to take over some of the kid's pea gravel play area so it'll be easy to plop it down there. I feel it's a good spot since the bed will be running north south and set against an east facing wall. Anyway, on to my questions:
1) What kind of soil do you typically find in Arizona? I know our house was built on farmland but no telling what the builder removed or added.
2) Is it best to dig down I few inches and mix this in with the new that I will be adding? I will be planting some carrots but I will probably go with a shorter variety.
3) What is best to fill in the raised bed? I was thinking about getting a 1/2-3/4 ton of screened top soil (about 4" depth) and add a few inches of compost. Does this sound about right?
4) Regarding the compost. I've got a few of those big blue bags of compost from Lowes. Is this the correct stuff to use? I feel this stuff is probably best if used on top of the soil and not mixed into it. It seems more course than the smaller bags of compost I've seen.
5) Finally should I add anything like Vermiculite or steer manure to the mix?
Sorry for all the newbie questions. I see a lot of raised bed posts but I didn't know if there was anything in particular that should be done for the desert climate. I would like to have all this set up in time for the fall planting.