I have a small lawn that is not it's best because it is used in the
summer as a patio area, the table, chairs and umbrella stand all turn
the lawn yellow.

I am thinking of digging it up and covering the area will gravel,
after putting down a mulch sheet.

I also would like to put triangular raised beds on the 4 corners to
grow veg in.

Questions:
How high would you make the beds?
I have plenty of home made compost, could this be used to fill the
beds?
What crops would you recommend?

TIA
Steve