Powerlifting Advice, Mainly Building the Squat

Hi, I have been training properly for powerlifting for about 6 months and have so far hit average numbers (all were recorded in comp in the 93kg class, I weighed in around 85kg):

Bench - 102.5kg
Squat - 150kg
Deadlift - 210kg

Basically I am struggling with the squat, I lift in Olly shoes with a fairly wide stance, I think I probably need to bring it in a bit to be honest. Anyway, a few questions on the squat, are you supposed to hold your breath as you decend into the hole, I say this because literally when I drive out the hole feels like im going to have an accident, anyone who has the same issue will understand that lol. I was thinking of ditching the Olly shoes for squats and just using deadlift slippers so I can be more on my heels, anyone else tried this?

At the minute I’m following a fairly basic program, once a week do 33 @ 80% for Squat and Bench (add 2.5kg per week), and another day do 32 @ 90% (add 2.5kg per week) on Squat Dead and Bench. The other training day I do more assistance/bodybuilding stuff like glute bridges, front squats, TB Deads stuff like that, (always more towards improving dead and squat). Also every workout contains a min of 50 Pull ups (altenate between very wide, and narrow, and grips etc) and also around 100 Tricep Dips, (hadnt done them for a while so stuck in the 15 rep range at the min).

Whats everyones opinions of this routine, ideally I want to hit a 500kg total as my next goal made up of:

Bench - 105
Squat - 175
Dead - 220

What would be your advice for attacking this?