Dumb beginner questions!

i’m an excited beginner to the fish tank world. I’ve had a Betta fish in a 5 gallon tank before, but that’s it. I just bought my first 20 gallon tank today, (tall hexagon) I think i rinsed the substrate pretty well before adding water (still cloudy but I assume it’s taking longer because it’s black sand?) i put in the filter and it’s currently cycling.

again i’m new to this so if anyone feels like sharing any tips or tricks i would appreciate any you have! No one in my life is into having pet fish so I’m sure there is common knowledge or unwritten rules i don’t know. i tried researching but i don’t want to do anything that could hurt the fishies!

i added 2.5ml of conditioner (the extra .5 was by accident) and some bacteria both Top Fin brand

i got the Top Fin starter pack so everything is that brand, not sure what to do with the (unopened) water heater as the thermometer reads just under 80°, which doesn’t seem correct but what do i know!

i really wanted to add guppies and a strawberry peacock and the employee at petsmart said that was a “great community” choice for my tank so i got excited but my research online shows it’s actually a horrible combo lol so im not sure what to add after the guppies yet. but i want something a little bigger and colorful like an orange or red peaceful fish

thoughts: -it’s weird how the substrate says triple washed and i still had to rinse it, glad i looked it up

-the above light to the tank seems so harsh, should i keep that off? or will they like it

-i don’t think i washed all of the fake plants before adding them in, is that going to ruin levels?

-thinking about adding a mystery snail with the guppies to start

-should i get a vacuum cleaner thing?

-i’m worried about reading water levels wrong, how often should i do that, and i heard certain types of fish naturally raise things like ammonia?

-is it true to empty 25% of tank while cleaning and then conditioning/heating the new water before adding it to tank?

-do the magnetic glass cleaners work?

-i hope my water testing goes smoothly because i can’t wait to have fish buddies!

TLDR: tips or tricks for a beginner fish mom of a brand new cycling 20 gal tank is appreciated!