Hard starting when cold can be symptom of many other problems, including bad reeds, worn rings/no compression, bad gas or water in the gas or float bowl, etc...
Also, stator failure is common on mid '80s KDX200s and one of the first symptoms is hard to start.
I had an '84 KDX200 (same bike as the '85) and it was a fun bike in its day. The stock fork springs are too soft - if it bottoms too easily first try adding some more fork oil (to about 4" from the top of the fork with the springs out and the fork compressed). You can also stiffen the springs by cutting a few coils off and adding some more pre-load spacers.
When new, brakes on the bike were weak even by mid '80's standards, so that is a weak point.
If the shock is in good shape, the rear suspension is pretty good by '80's standards. However, linkage bearings need to be maintained - if the bearings start running dry, you might damage the Uni Trak rocker arm, and replacement parts could be hard to find and expensive.
If running right, the motor is decent and it was considered pretty strong for an aircooled, non powervalve 200cc bike.
The overall strength of the bike is its light weight and good handling. On a fairly smooth, twisty trail an '84 KDX200 can keep a pretty good pace even compared to a modern bike. You will be at a disadvantage in the bumps and jumps, though.