If you want to start out with a pop-up, I think that is what you should do, especially if you are younger and have younger children. We started out with pop-ups years ago while our boys were young and had a blast. We took several month long trips out west in the warmer months. It is more like outdoor camping which is what many really enjoy. We now have a 37' fifth-wheel with all the conveniences which is nice for us "older" folks, but some of the fun we had with the pop-up is missing.
Like us and many others, you probably will upgrade to larger, more self contained units as time goes on, but that does not mean you should start there. You will miss some of the basics and the enjoyment of the outdoors if you do. Pop-ups are more economical, easier to tow, and you can park one just about anywhere. The last 2 we owned had roof air, heaters, and small 1. 5 cu. ft. gas/electric refrigerators.
We have had a Starcraft and two Jayco pop-ups and all were good units. I think most of the major RV manufacturers that make pop-ups have decent units. If you can find a used one a year or two old you can probably save a bundle and there is relatively little to maintain on one.
Go for it and have a ball!!!
Jim