Sorry, this is a re-post. I wondered if this would be more likely to get answered over here.
Thinking about buying a inexpensive 29er or 29er plus single speed. Figured I could us it as a winter commuter, play with it on the trails, have it as a spare bike and maybe set it up as a grocery getter. Who knows, if I build a IGH, It might even be a good daily commuter. So based on your knowledge, experience and opinion, 29er or 29er plus SS.

2 > 1

Those two are a good start but you neglect 650b and the good ole' 26" plus all of the various fat and mid fat sizes and let's not forget the different genres of mountain biking so you really should budget yourself for 20-50 bikes or so just to be on the safe side. You wouldn't want to be doing some all mountain stuff on a cross country bike or worse try to take a mid fat bike in some really snowy conditions.

N+1 my friend N+1

I can only ride one at a time. "A man's life does not exists in the abundance of his possession's".

You can only ride one at a time. But you can own more than one. I have 4, and that is barely enough.

Only 4 ? You've got a long long way to go before you've got enough.

I'd go straight 29er rather than 29+. More versatile in my opinion.

Thanks for the input. I struggle spending money, even when it's plentiful. Never had a single speed. I know I want a 29er. Learned the value of bigger wheels from inline skating. Like that the bikes I've looked at had solid front forks. I'm sure it will be challenging to ride a bike without gears.

Yes and no. It depends on your willingness to strain yourself, walk your bike, do maintenance, etc. I don't mind walking when I have to, and after 40+ years of wrenching on bikes I'd rather just ride now. So I have two singlespeeds and nothing else.