If you were to test your rep maxes do it before you start a new cycle, after your deload week. There's no need to test your 1RM often. If you're getting stronger on your sets, your 1RM is going up as well. As for your "noob gains" don't worry about them. A few of my friends and myself have made the mistake that these 5-10 pound jumps are too little. We wanted to get stronger and bigger faster, so we ended up switching programs every 2-4 weeks and it was stupid, made shitty gains and felt like crap.
Don't be like us. I understand not seeing super 40 pound gains every two weeks seems bummy but, 10 pound jumps every month? If you started out squatting 135 for 5, in 1 year you'll squat 255 for 5. Add another year and well, you can do the math.
As for assistance exercises, do whatever and see how your body reacts to them. It's all trial and error, we're not you and you're not us. If something is hindering your main lifts, lower its intensity/volume or drop it, if not keep doing it.