I copied and pasted your question in an email to my husband. He isn't big on these kind of forums but I know how much he loved Pikes Peak. So here is his answer. I hope it helps!
Andreia

Good grief! Relax for a moment... Items 1 and 2 were more like items 1 through 20. First
things first (Your second item): Running Pike's Peak (I am assuming
you mean the ascent, only) will only make you stronger and faster. It
certainly isn't speed work, but you're using your quads and hamstrings
in a different manner than you do on the flat, so it actually simulates
speed work without the damage. If you are planning on doing the
round-trip, I would advise against it. The ascent is only 14 miles but
your time will be comparable to your marathon times on the flat. If
you ever want to get stronger for a marathon, run hills or stairs
(assuming you don't have hills). You should be over any weird stress
or pains within thirty days of Pike's Peak. Second
(your first item): You do not need to run trails although in might be
nice to do. Find the best incline you can and do "hill" repeats. No
kidding, running stairs will simulate the same pain that you are going
to have for nearly four hours at Pike's Peak. You probably won't be
able to do stairs for four hours, but you need to be doing one hour
sessions once or twice a week. I know...boring!!! Finally, the
biggest problem is that you are at elevation and you will be in oxygen
debt immediately. How well do you handle lactic acid? If it is a
problem for you look at doing hard intervals on the track with short
recovery periods. Work up to 90 minutes on the track. Your body will
respond more favorably when you are sucking up all the air you can get. Finally:
Plan on a mix of running (ha!) and walking the last one to two miles.
It is very steep, it is above 14,000 feet, it is very rocky, and cold.
Sometimes fast walking is more than your body will be able to handle.
Other than that it is total fun. It is one of my all-time favorites, even more so than Boston!