I'm going to try to teach myself guitar over the summer and fall. anyone got any tips for a beginner?

Practise everything super slowly first, to build muscle memory. Always push yourself, never be content with power chords only. Learn how to hybrid pick as earlier as possible. Practise finger independance.

Don't give up and make sure to use vibrato and bending to make your playing come alive.

Guitar, Bass, Trumpet, Drums, Piano

I want to learn another but i can't decide what

Yes.

Seriously though,
Guitar, bass, piano, cello, viola, violin, and harp.

Bass, guitar, drums, keyboard, and didgeridoo. I also own a harmonica.

I've been playing violin, viola, and cello since the sixth grade (seven years). I'm now playing bass and some viola in a band, and I absolutely love it. I just picked up the bass a few months ago, but it's been super easy to get used to.

guitar, piano, trumpet for 5 years but dropped it last year.

lol trumpet's pretty hard to keep up ><
6 years for me in a month

Piano (by far my best instrument), Drums, Trombone, Vocals, Bass Guitar (I'm just picking this up, if anyone could spare some tips, please do).

For a starter model, go for an RBX170
It's very nicely made, and it has a jazz and a precision pick up and you can solo one with the EQ controls to get a bunch of different sounds

Also, it looks cool and comes in a bunch of colors

Not about what I should buy, but about actual playing; I have a bass already.

Use all four of your fingers to press frets so that you don't get into the habit of just using 2 or 3