Diet is Main, Supplements are supplemental. If your diet is on point, supplements will help. If you diet is not on point, no amount of supplements (at least not legal ones) will help you. You can't turn a hypercaloric diet (where you eat more calories than you burn) into a fat loss hypocaloric diet with supplements. You can't turn a hypocaloric diet into a muscle building hypercaloric diet with supplements. Keep your diet on track and then worry about supplements, if even then!
Main lifts are Main, Accessories are supplemental. Don't get too caught up in the extras. Concentrate on the big movements - hip hinging, squatting, pressing, pulling, jumping, and core stability. Carry heavy stuff. Then you can worry about some extra ab work and biceps curls and calf raises and so on. They don't build the most muscle or burn the most fat, so leave them for after.
Intensity is Main, volume is supplemental. For most people, anyway - it matters more how hard you do it more than how much you do it. Work hard before working more.