Acquired Greenhouse

We bought our house about a year and a half ago and this greenhouse came with it. I planted my first garden last year and learned a ton, and this year I’d really like to learn how to properly use the greenhouse, especially since I’m in zone 3b.

Right now it only has one older window on the back side for ventilation. Last summer I moved some of my indoor tropical plants into it and they did okay, but I had to remember to open the window every morning and close it most nights so they wouldn’t overheat or get too cold.

This year I’ve also started a bunch of seedlings indoors in a mini greenhouse setup with grow lights, and they’re doing really well so far.

I’ve been reading a bit online and keep seeing recommendations for things like automatic window openers, heaters, fans, or even barrels of water for thermal mass/heat retention overnight. I’m trying to figure out what’s actually worth doing for a beginner in a colder climate like mine.

A few questions:

What are the biggest upgrades or changes that made the biggest difference for your greenhouse?

How do you manage temperature swings in spring/fall in colder zones?

Are automatic vent openers worth it?

Any beginner mistakes I should avoid?

Also, is this the right sub for this kind of question, or is there a better greenhouse-specific community I should check out?

Thanks! I’m excited to learn more this season.