1.) Do you unstring it or not? How often and Why?

Sometimes yes, other times, no. In my house I leave them strung if I'm going to shoot them in the afternoons even 2-3 times a week. if I am not going to shoot them, I unstring them (recurves and longbows)

2.) Why can't you use certain strings on an older bow? Like the Dyna Flight 97 or whatever it is called? Isn't a string a string?

I think it has to do with the limb tips.

3.) What is the difference between 3 and 4 feathers? What about broadheads? Will it affect the arrows flight if you use a wrong combination of head and feather?

I don't believe so, no. I've fletched arrows RW and LW both using the same RW jigs with no apparent affect on flight. Don't mix the feather though. See below comments on arrow tuning. You broadheads will most likely fly fine if your arrows are tuned to your bow.

4.) Do you pratice with broadheads or use field tips? If you use field tips how do you get the weight up to 8 grains/lb?

Both. My concern first and foremost is arrow flight. If I get that down, then my accuracy will also improve. Then I can worry about total arrow weight and FOC.

5.) And tell me EVERYTHING!!

Longbows/recurve are simple compared to a compound. Simple to shoot that is. Start with a full length bare shaft and shoot it with a 125 grain field point at a target. Watch the flight. If it flies nock right its too stiff, nock left too weak. Most likely you'll be nock left, so cut 1/2" off your shaft and shoot again and eventually you'll find a length that'll fly really straight and pretty from your bow (assuming your nock height and brace height is good)

From there fletch your shafts at that length arrow and go shoot and have fun. Consistancy is THE most important thing on your shooting as far as form. Even with great form you'll still have to have concentration though, and a great release. Without either of those 3 you'll not hit right where you want to. Ahhhhhh, but when all 3 DO come togehter, its a beautiful thing !

Have a lot of fun, buy some judo to stump shoot. I roam my neighborhood shooting pop cans and stuff.