I want to buy a mountain bike is a 23.5 inch frame big enough for a 6'1 person?

It all depends on your inseam and your arm length.Your torso could be a factor as well. I suggest going to a good bikeshop and tryout some bikes.They will help you find the right size for you. Yo...

Stick with the hardtail type. Specialized: Look at the Rockhopper line Kona: the Blast line

I love to Mouton Bike You get what you pay for so if it's over 300 Buy it make shore to check the arch on your Back and quality of the Rims make a Huge Difference .....

You can use mountain pedals without any problem on road bikes, so you could have the same system on both bikes, just don't show them to your roadie friends ;)

I think KHS Bicycles are the best bang for your buck out there

Yep...15" should do for most frames. Try out a couple of larger ones just to see how they feel, though. A 15" will also be sold as a "small" by most companies.

i dont know, but the last time i rode a bike my whole body ached .

Iron Horse's complete line has some low grade bikes and some very good top end rides. Just be careful what you end up with, check the component level and be wary if getting it from a box store...