humble monthly is it possible to only get one month and stop?

yes, just immediately unsubscribe and you will still get the unlocks at the end of the month but not be charged for the next one.

yes, it is.

Yes, it's also viable to subscribe then remove your payment info from settings to avoid being charged in case you forget, then stay subscribed until near the end of the next month's payment charge so you get 10% discount for near 2 months instead of one.

You get a 10% off on HB Store while you're marked as 'subscribed'. They would normally charge you on the friday 1 week before the Monthly is released (it's released on first friday of each month), so for this month they would charge you on Feb 25th. As long as you go to your settings and unsubscribe before the 25th you keep your 10% off and won't be charged anything. Then if you just don't care about the 10% off you can unsubscribe right now and just wait for your games to show up on the 3rd of march without worrying about next month.