Looks like my neighbor, who is a construction framer, and I will do virutally all of it. The county chief bldg inspector lives right across road from me and has given some advice too.
Adding to my double wide mobile home. Full width room at one end.
I've done just a little construction myself but wouldn't attempt it without lot of good advice and experienced help. Searched online and found advice there too -- such as not to try to get the floor level to match exactly the existing home floor. Had worried how we were gonna get that just right, but thinking about it, it'd be fine if there were a few inches of up or down step going into new room.
Thought I'd rent a trencher to dig the outlines of the footer -- then dig rest out by hand. Then lay one or two courses of concrete block on the footer -- placing lag bolts in concrete in the blocks every 6 or 8 feet. Then bolt down a pressure treated 2 by 10 on top of the block. Inner piers will be just prefab concrete pads with those pyramids with slots.
The neighbor and his friend can floor it and frame it up from there.
This is the design I have in my head anyway.