You do need to check local codes. In PA, they wanted a pad poured at
the bottom of a 36"hole, as there was a frost issue. I also picked up
a very useful book that gave deck plans, strength for spans, etc. I
worked from that, and submitted the plan to the local zoning officer,
along with photocopies of the pertinent tables, etc. No problems.

As to free-standing, I'd go to attach to a plate that is lag screwed
on to side of house. More stable, and you can reference everything off
of that. I ended up putting a hot tub on the deck a number of years
after I built the deck, so was quite glad that I had slightly "over
engineered" the deck to take the load of the hot tub.

Local code required that I build it strong enough so that if I ever
enclosed it, that it would stand the load. Good idea.