If you get a firehoop, go for one with removable-spines. If you're new to firehooping, I'd recommend Quick Wicks (beware of the knock-offs)
I'd imagine that you should just get the same tubing that you are comfortable with now and however many wicks you want. As for price, the only way you are going to be able to get a hoop under $100 is to buy a used one from someone (check the shop on this site) or make your own.
What I recommend to my customers is to order the smallest size hoop you're comfortable spinning without fire because the wicks will add both weight and effective size. The biggest problem with hooping a fire hoop is not realizing your effective radius and smacking into things.
As for the rest, given the option, most people go with either 5 or 6 wicks. Personally, I prefer 6 because of the balance and symmetry (the hoop can break down into 3 identical pieces, etc). But 5 does give you a little more room between spines to do outside tricks. Personally, I don't understand why more first-time buyers don't go with a 4 wick hoop.
Ya, I started with 4 wicks, and that is just perfect for me at this point! I feel comfortable grabbing the hoop because of the space in between, and it still looks really neat in my opinion.
I got quick wicks! and I highly recommend them. It's a great product for fist time fire spinners, if you get 6 and find your not comfortable then go down to 5 or 4, you have options, another great thing is if you don't want to spend the money on all 6 then get 4 to start then save up some more for the other 2.