It should be easy right now but trust me when I say 5lb per workout will start adding up quickly. Right now while it's easy you need to focus on keeping very strict form. This will burn the proper way to do these movements into your mind and hopefully as it gets heavier your form will not break down.

Try to weigh yourself at the same time of day each time. This way you aren't trying to account for what meals you've eaten, water you've drank, etc.

You can add ab work if you like. I do hanging leg raises to compliment my squats and deads. I would say if you're going to add it in then just make sure you're doing it after your core heavy movements.

I would recommend pull ups over lat pull downs (any day ... hands down) if you have somewhere you can do them. A much better exercise in my opinion.

IW