I took a few days before "officially" starting and tried out different weights. With your first set of 12, it shouldn't be any more stress than a fast paced walk, then add in sequence. So adjust your starting point accordingly. Do that for a week or so, and keep notes.
If you use dumbbells (or cans or bags of sand/water or whatever) you're mostly OK without a spotter. Anytime the bar or dumbbell is over your head or face is the most dangerous, so use caution.
Congratulations on getting started.