another post, but i couldn't remember everything you said, so to the second part.
when connecting one section of rail to another, where will be a gap of some sort. however, 9 times out of 10 it will not be a problem. just set it up so that your edge will not catch the front of the next rail when transitioning from one section to another. what i would do is just set up the end of the first rail just above the second so there will be a small drop, but its not noticeable and you will not catch, you know what i mean? i have a flat backyard and tried to make different rail setups but kinks don't go well on a flat surface, so again, if you have a flat backyard, just forget it and build a flat rail. i tried to do things like down flat, or flat down, and neither really worked great. once i made an a-frame and even on snow from a 6' tall drop in, i had no speed going over the top. as for the supports, it depends on the height of your drop in. if the lip is a foot off the ground, you will want it around that height. remember, you can always put something under the rails to make them taller but you can't make them shorter. if you really want it to work well, make extenders (of some sort) to the supports of the rails that will basically add on the rail and make it taller.
sparknotes: if you have a flat backyard, DON'T DO IT. if your yard is on a hill, you are golden, just make everything legit and you should have no problems with what you want to do.
"When the kids are looking for style, is it within their own minds, or their peers' minds?" - Warren Miller
have you felt this pan?
you need to diversify yo bonds n*gga