New/Old trying this Scale crawler hobby

[TEANINER]

It has been a while for me in the Hobby world. Last time I played with them was when Losi Mini T's were the big thing. I knew them like the back of my hand with fixing and rebuilds. Married, Kids, and Divorced. Kids are a little older and I was hoping to get them into RC. But I am going to dive into it first with what I want. A couple of questions I can't seem to find the answers to.

1. I understand Rock Crawling and scale. what are the speeds of these trucks? I am not looking for fast bullet speed. Just wondering when I hand the controllers to my children (10ish) will they enjoy a little ripping around the back yard?

2. Looking to piece together a Scale Truck. Reasons of not spending a bunch of money at once and have some fun building the truck. Like I did with my Mini T's.
Do a lot of the parts of the chassis work with all models? I am assuming with the adjustable wheelbase that most bodies will work with most chassis? Looking at the Axial SCX10. What are the chances of finding a good amount of parts to make it work? Not looking to go full custom and make my own parts. But build it slow and pick some cool parts or buy some kits that are not complete. Do I pick a model and just stick to those parts?

3. I own some land and a steep hill going down to a river. What are the chances of the hill being to steep to crawl along it? There are some deer trails on it. Hoping to be running along the hill for some fun.

4. I have been watching some videos on youtube. Is there a ideal weight to shoot for? Heavier or lighter?

5. I have more questions but these need to be answered and then Ill get after the rest thru some research. Been looking for about a month and this is the first I ran across the website. I seem to always just find the Hobby stores but not good info. Where do I look for the full on deep zone of scalers?