Do you have a squat rack? Or else it might difficult for you to squat with a barbell. Unless u learn how to clean and do front squat.
If you are really newbie, i ll suggest u to squat bodyweight -> Dumbbell -> Barbell

Instead of buying barbell and the weight plate, i think invest in a gym membership might be cheaper.

Don't worry about that. Just use mixed grip to deadlift. Deadlift main purpose is to train your whole body and not just your forearm. Why should you restrict yourself to deadlift heavier just because of your weaker grip strength? But IMO, mixed grip should be enough for you to deadlift a really heavy weight. If you feel grip strength is the reason for your plateau no matter what grip u using, go and get a strap. Just train your forearm directly after your deadlift session if you worry your forearm is lacking.

And also you shouldn't use "momentum" when deadlifting. Deadlift = dead stop on the floor and lift it. You shouldn't include any momentum at all or you just waste the purpose of "dead"lift.

Try avoid wearing cushioned sport shoe to squat. It makes you so unstable and shaky during whole squat session. Wear hard sole shoe like converse or just squat barefoot if you can't afford squat shoe. Either improve your ankle mobility or just invest a squat shoe will be better option than squatting on weight plate. I did that before but as weight goes up, you are increasing your chance of injury due to accident.

Depth seems fine and just hit parallel.

But when you lowering your body, make it as a whole movement. Don't separate upper body and lower body. You are lowering your upper body and bend your knees after that. Do both at once and not doing it separately. You only did this correctly during your first and second reps.

For your first reps, always take a big breath and brace your core before you start squatting. Control the weight and don't rush.

Don't think you can get it from any local store. I bought mine from china. I think you had to search around the net.

Never tell darklight that high carb is bad lol...