You may start warming up with an empty bar and keep on adding 20 kgs (total weight) till you reach your work set. No need to rest between warmup sets (you'll get some rest anyway while adding plates). I think in SS the max we can/should rest is 7 mins, if you need more rest maybe you need to eat more or do something else/go advance etc. I'm not an expert, wait for a coach to give inputs.