New players don't seem to be quite sure what to expect/how hard to push a tower, and it's hard to figure out until you've played a bit of the game, so this should set some basic expectations on some things easy to get with extremely low requirements. This is chapter 1 and 2, as towers after that have radically different requirements ranging from over 200 sunstones(heavy) to a moon with 0 sunstones and 6 badges and a massive overscore of 17 or 18 sunstones(glitter, thanks zyolex), and by the time you're delving that deep, hopefully you're in the discord to ask us more questions.

Tactical Tutorial(aka Tutorial 1) - Gold
NEW - gold
D - gold
K - most people get bronze, but theoretically maybe silver?
mini - plat
G - gold, maybe plat if you optimize enough.
Tutorial 2 - Silver
Dojo - Plat, thanks Phoil.
Tutorial 3 - Gold, plat possible?

Towers you should probably have some sunstones before doing:
W - Not sure, silver should be accessible, but probably as high as gold.
P - probably silver
Pop - bronze or silver. if you can somehow survive through to clear 2 then as high as diamond.

Honorable mention that technically isn't in any chapter:
Ruin of the Sorcerer - +5, +4 isn't tight. Scores as both pure and impure simultaneously, so if you drag its folder into your Nexus folder you get doubled sunstones(devs know, seems to be tacitly approved). This tower is probably the best tutorial tower to dip your toes into orbs, equipment, and general gameplay considering it's short, simple, and +4 is available with several strategies.
To get this, go to the Team Nexus website and download it.

I probably won't ever be updating this guide, so it'll eventually be very outdated, but since it's only meant as an easy to see rough reference don't take it too seriously. This game requires you to learn to make your own judgements about where you sit when working at meta progression, so learn to trust your instincts and you probably won't even need to care about the quality of this guide 2 or 3 towers in. Every sunstone counts, cherish every one.