I would do 5 sets for the big lifts. I'd not go above 5 reps per set for deadlift (just conventional, not the romanian), and do sets of 8-15 for everything else.
For arms, shoulders etc I would just do 3 sets, again 8-15 reps.
Tabata or some other HIIT is fine after your weights, but in my opinion you should prioritise the weight training so if you only have the energy for one, do that.
Planks are perfect for your core. Don't be scared to try more challenging variations when you can hold them for a decent length of time.
Your coach doesn't know what he's talking about, which is all too common in the world of personal trainers, unfortunately. Your diet will dictate whether or not you "bulk" but considering you've lost 100lbs already it sounds like you're doing fine with that.