Hi Bruce.

1.) Can you use the FSX Flight planner and import the flight plan into the CS 727 and will the CS AP follow the plan? I have never used just the NAV radios or DME or ADF to navigate. I either fly GPS direct using the AP, or just let ATC guide me IFR.
Yes you can. I do it all the time. I usually select a High Altitude airways plan. Note. You will probably need to add a NAV/GPS switch to the Autopilot, or at least create a keyboard shortcut for it. I use SHIFT + N.

2.) Do you/can you use the FSX fuel and load planner? I saw the CS load planner, but didn't notice a fuel planner.
I use it. For short flights, I have the same quantity in all three tanks. There is no CS fuel planner foor the 727.

3. For someone fairly competent with the FSX default systems how difficult is it to learn the CS 727? What's the learning curve here?
That's a hard one for me to answer because I started using flight simulator back in 1983. BUT. Up until the middle of last year, I was a GA Flight Sim pilot only. Now I love these airliners.

You can come in here to ask for help and advice. Most of us will try to help you to achieve whatever it is that you are trying to do.

I hope this helps.

Mark