Outstanding little machines!!
The 100/125cc Honda engines will run forever and ever, as long as you keep plenty of good clean oil in 'em. The cam rides right in the aluminum of the head, and if they starve the top end for oil, you're lookin' for a new head. They had no oil filtration at all, other than a centrifugal 'slinger', and about all THAT does is separate the heavier chunks...
Otherwise, it'll fer sure haul you around at 45mph or so.
My family has owned 4 or 5 of 'em over the years, and my older brother and I used to go boonie-bashing together on a '75 XL100. Identical motor, just different 'styling'. XL's are dual-sports, and CL are the high-piped 'street scrambler' styling.
And, if you really want to breathe on it, there's a whole world of hot-rod parts, thanks to the AHRMA 100cc class - bore kits, stroker kits, cams, valve springs, and they respond really well to even mild port clean-up.
As for forums, there's ThumperTalk at
http://www.thumpertalk.com/forum/ They have a Honda section, and a Vintage section that has PLENTY of enthusiasts.
There's also an XL Forum page at
http://forum1.aimoo.com/XLBoard Lots of good advice there, too, but kinda slow, posting-wise.
Have a ball! And, of course, post some pix of your new little guy!
Kirk