I'm planning on running a large number of 'play-by-post' games (not all on this site) and updating while doing other stuff.

I think 100 one-shots, or somewhat less if some of the games are a campaign.
As I'm new to this, I plan on messing up constantly, and correcting problems when they come up.

I've read 'index card rpg' and 'the lazy dm', and am planning on determining plots/scenarios as fast as possible by using a combinations of random rolls with charts and a loose framework. ('reskin' stock plots/characters, 3 npc encounters, 3 possible combat, 3 secrets, etc.)

Also: for the above paragraph, I don't plan on anything going as planned, and to roll with whatever the players do.

I'm planning on using cheat sheets and the books directly( call of cthulu and dnd 5e at this point) for running games.

So...
Am I on the right track doing something like this, or is my time best spent doing something else?
Any additional advice to a new dm?

Thanks to all replies in advance!