I see no reason for not starting with a TT. What I would recommend is that you buy a used unit at a price that is well below your budget. Then go out and learn. In a few years, you'll know better what you want and can upgrade accordingly.
For this reason, I would also buy a bigger truck than you think you need. You aren't familiar with RVs, so what you end up with can be very different than what you thought you wanted.
I would not start with a popup if you know you don't want one. They are far more like car tent camping than RV camping having to move things around, setup and take down, etc. If you know you want a hard sided, then start with an inexpensive hard sided.
I started with a cheap TT. Under $2000 and it needed lots of work throughout. But, it taught me about the systems much faster than a "quality" TT. And in 3 years, I was able to sell it for what I paid and but the rest of the expenses down as entertainment and educational expenses. Since it was not a brand new expensive rig, I didn't feel worried about trying to fix things myself and messing it up.
