Ha, Marje, we have one like that at a club I go to: not a bad guitarist but turns every song into a "talking blues"! And others who sing unaccompanied but change key at the drop of a hat, throwing the self-appointed "everyone's accompanist" right off track! (Sometimes I wish he would just shut up anyway!)
But back to the point, yes, I agree, it is good to sing on one's own or in a group, without accompaniment, until you are confident in holding a key. The acid test is to play your key note before starting and then again at the end of a song: they should be the same. I find I'm more likely to drift upwards in an up-tempo song and go flat in a slower one.
And as for playing a singing at the same time: this does only come with practice and familiarity with - a bit like driving a car, when you can stop thinking about how you change gear (analogous to changing chords on your guitar) while you observe the road ahead (sing your song). I know it was quite a long time after I took up guitar, and later, button accordion, before I could play and sing at the same time: too many parts of the brain having to go into overdrive at once!