Hello all
 

Hi, I recently took up MTBing in the summer and having just started road biking.
However there are few obstacles, my budget only allows for the one bike (for now) and thats the mountain bike (FS)
So im going to ride this thing until the snow falls at which point im going to the gym to use the exercise bikes (i use the "Hills - Around the World" setting) and maybe get a new (road) bike around christmas (i might build one, i dunno)
I'm just wondering what tips and advice you guys have for me because im not really a full roadie, but the goal is ultimately the same
should i get slick tires? how much are they?
is there any way that i can lock the dual suspension (at a low cost) to make the bike more efficient?

how can i get a road bike (nothing fancy) for under $600 (CAD)? i dont mind buying used, should i lurk garage sales? would a really old road bike be much more efficient than a new MTB?

also, id appreciate any tips you guys have for helping me get my legs a little more built
im 16, 5'8.5" and only 130 lbs
im want to gain weight, but i refuse to stop cycling

i know this is kind of all over the place, but i just need all the help i can get, cause my mileage is increasing every ride but i know in the back of my mind that i could be more efficient

I think if you eventual goal is fitness, there's no point in making your FS MTB more efficient. Once you're in a condition to ride that fast, you'll undoubtedly ride a road bike even faster (once you get used to the different posture on a road bike). For you price given, I think it's best that you look for a used road bike. If you want to build up your legs for cycling, then ride more. Of course cross training never hurts.