I guess it all depends what you want to do and if you think that you will want to trade up soon or not.Only you can ultimately decide what is best for your own individual situation.
From and observer standpoint,...you have been through a few street models and learned to accel and improve your riding requirements (for your personal satisfaction of riding)...
This only leads me to beleive that you would probably rather start to learn a few proper off road /mx riding techniques and advance a bit(for that same personal satisfaction).
To do so on a kx100 would be futile and would have to be traded in short order at 190 lbs.There is nothing that compares to MX suspension...It MAKES you a more confident ,faster rider...because it does not throw you off the bike like enduro suspensions.
As for the ride height,any suspension shop can lower the rear by installing a small spacer on the rod in the rear shock,...even space down the front forks,etc...and sometimes use lowering links(I personally don't like those as they always seem to have adverse effect on geometry.)....but often they use the proper spring rates in the forks and shock(if the stock ones are wrong for you)...and set the sag and valving properly,and the bike settles in nicely. Also many do some custom shaving in the front portion of the seat foam.
....but don't get too hung up on the still height of a real full sized mx bike. EVERYBODY is too short for them...you get used to that very quickly. Many very short rider even prefer to not to lower,as they want full complete travel of the suspension,but many also lower it for comfort,based on their intended use.Ricky Chamichal is TINY and short!
Another thing to consider,is that you will probably seek to learn riding technique...in reading or taking lessons you will soon learn that seat height is of little importance,as 95% of the time you are supposed to be standing up...yup,95.
Even advanced enduro racers know that standing lowers your center of gravity and makes the bike go thru the gnarliest of ruts...that would be absolutely impossible to go thru without wiping out if you were to sit your butt (and your weight) on the seat. Actually,some Motocross instructors make kids drive the first day with he SEAT REMOVED....so that they learn to master the basic important feature of proper off road riding technique of a low center of gravity...true.
You actually spend alomost NO time on the seat in competittion,except after the apex of a turn,and to get traction to get moving again....then back up on the pegs.
I realize that all this doesn't apply right now and you just want to get out and trail ride and have fun,etc.
...but I would just bet that you would regret a 100 after a very short time.
Like I said,fun is the important part,and ultimatly,only you can decide...just giving input.