Questions about radon mitigation

Hi All! New homeowner and new to this forum. I have been doing a lot of research on radon since buying my first house last fall. The results of the inspection showed I had a 4.2 pCi/l radon level. I believe this was a short term test and so I had a long term tested performed to see the "actual results." This came up with nearly the same results (4.6 pCi/l). I know the level isn't too high, but it is above what is recommended. So, I'm going to do something but am hoping to get a few questions answered first.

1. What is the easiest way to determine how much cfm is needed? I have a Split-Level 1800 sq. ft. home, 700 basement, 500 Main and 600 Upper Level. My sump pit is in the crawl space with a fairly easy exit point, except for a deck on one wall. Therefore, I would rather run the pvc a longer distance (15-20 ft, 2-3 elbows) and exit out the back since I plan on extending the deck to the front of the house as well. All the radon fans I see don't have very high cfm ratings, but have a high inches w.c. reading. I assume this is because it just needs to create a "better" negative pressure reading than the house does? I have an HRV and a new 90+ furnace that brings its own make-up air in, so my house shouldn't be too negative???

2. What is the better procedure; Mounting the fan inside or outside, and why?

3. This brings up another question; Is there a reason I couldn't terminate the pvc out the wall (fan inside) and not above the roof line?

I'm sure I am forgetting something but for now this will do. If any of you can help me, I would appreciate it!

Thanks,
John

Try, Radon | Indoor Air Quality | US EPA.
The pipe needs to extend past the roof line to help equalize pressure if the fan fails, and to exaust the radon higher if possible.
The entire basement needs to be sealed, sump included.
As far as how your house is pressurized? Only a blower door test will give you results you need.

As far as DIY on a radon system goes, it is better left to the pro's. This way there is documentation for a future owner when you go to sell. Folks are funny that way. Otherwise you run may run into to many issues.
Good luck.

Thanks inspector, I'll check it out.