Getting ready for Community Day

Do not evolve them during Community Day! The opportunity cost in caught Larvitars is just too high.

Without knowing what your bag space is, I recommend the following:

Evolve + transfer 20 mon for every half hour you intend to do community day, then transfer anything else that you don't see a long term use for. That level 17 93% Masquerain? Do you have a reason to keep it? See if that gives you enough space. Evolving 1/2 hours worth not on a lucky egg is still 35K xp give or take, which isn't bad. It's just 35K less.

Also consider if you have the coins to buy more lucky eggs - they're not terribly expensive as items go, less than 2 days worth of coins.

First look at which way you get the most mileage out of your lucky eggs.

Mass evolving with a lucky egg nets you 1k exp per evolve, which amounts to 60-80k exp per each.
Catching during the community day with a lucky egg nets 600 to 1560 exp per catch, with a reasonable expectation being something like 1100 (between 960 and 1260 for great curves with or without first throw bonus). So you'd have to catch about 60 pokemon every half an hour to make the amount of exp equal.

So if you expect to catch less than 360 mon in total during the community day, you should use your lucky eggs for mass evolving instead, no question about it.
If you're expecting to catch more than that, I'd recommend to just trash your evolvables to make space, the candy for them isn't going anywhere and you can always catch new ones after the event.

Whatever you do, remember that this is the most important community day we've ever had and you want to prioritize those Larvitars over anything else, including your exp gains.

You could simply transfer all the disposable pokemon without evolving them. You will keep the candy and use it to evolve other at a later time in a proper egg session. The factor limiting the number of evolutions you can do is candy, not starter Pokemon, as even for pinaped Pidgeies you need to catch two in order to evolve one.

This way, you will not loose any XP in the long run and still be able to make full use of Community Day.

I transferred a bunch of "unique" Pokemon I had no use for. Why am I going on to a pidgeotto or kakuna? Once you do that, it should open up space. If you're literally full on starters for evolves and rare Pokemon and fighters/defenders, you should look at buying Pokemon storage.