I always start with just the bar and keep adding every time until I hit a plateau. I don't do stronglifts right now (just VR training) but something like 120 kg in squats and 150 kg in deadlift last time.

Normally when I hit the wall I transition to a regular split program with biceps curls and whatnot, which I find much more stimulating and fun but it's still a chore compared to VR training.