In terms of the rollout of N64 games, yeah, assuming the current one per month rate continues, there's enough now to get to June (i.e. Majora's Mask in February, Kirby 64 in March, F ZERO X in April, Mario Golf in May, Pokemon Snap in June). If Nintendo were to announce the next block of games in a June Direct, or as a standalone announcement in June, they could announce another 7 games to take the service through to January 2023, e.g.
July: Wave Race 64
August: Mystical Ninja Starring Goemon
September: Mario Party (GB/GBC NSO launches around this time)
October: Castlevania 64
November: Pokemon Stadium
December: 1080 Snowboarding
January: Harvest Moon 64
(Obviously these aren't concrete guesses at what's coming this year - just an indication of the kind of games which might pop up - I suspect the actual releases might be more popular and include more Rare titles; Diddy Kong Racing finally being re-released would be pretty special, and Goldeneye rumours abound)
By January 2022, they could have 23 games available internationally. Assuming Nintendo continue one N64 game per month for the foreseeable future, they could then use a January or February Direct (or just drop a trailer) to confirm the next set of games (5 would take them to June 2023; or 8 to September 2023). It might that Nintendo slow the rate of releases around September 2023, given steady monthly releases would bring us to 31 games and there were 38 slots in emulator.
Of course, they might have negotiated more licences by then, but I still suspect we'll see the monthly release rate stop after 2 years. My assumption is September 2023 potentially marks the debut of GBA on all Switch hardware and GC on more powerful hardware, with a monthly release or two for GBA and a GC title every other month, or something like that, combined with another price increase.
What's more difficult to know is how Nintendo intend to handle Mega Drive. The first update was big, but I can't see them offering 5 games per month; the emulator has 55 slots and so we'd be out of Mega Drive updates by the summer at that rate.