Hi Mat,
first of all, I believe fork tines are HIGH carbon steel so some thought should go into what rod you use to weld your top plate to the middle upright section.
your other pieces of material are most likely low carbon steel. I would bevel the upright section on both sides at the top and bottom.
I suggest you ask a local welding supply shop for the right rods, also they will be able to tell you how much to pre-heat/post-heat and whether you will need to wrap the weldment to slow the cooling and prevent cracking.
With the bevels and the size of materials this welding job will be time consuming so taking it to a pro might cost quite a bit. There's no reason why a novice couldn't weld this, you just have to have the right procedure, enough time and enough rods.
Goatee