Hi. Most any bike is designed with a rider in mind of average height, weight and riding skill level. If you weigh 150, then you will weigh from 160 - 165. Unless you ride naked, you need to worry about your weight in full riding gear when discussing suspension issues. Also, if you plan to carry any tools or a water backpack (CamelBak), add that onto the 160 - 165. The KDX comes stock with an unbalnced suspension setting. The fork springs are a good bit softer than the shock spring. If you were taller and had no desire to lower the bike, you would be better off with new fork springs that are a little stiffer and a new shock spring that is a little bit softer shock spring.
If you are wanting the bike to sag more under your weight, then a softer shock spring is in order. You can probably get by with the stock fork springs for now. Later on you may feel more comfortable to go faster and need a stiffer spring.
The best, but most expensive solution, is to have travel limiting spacers installed in the forks and shock. These, along with the corrct rate (stiffness) fork and shock springs for your weight, riding skill level and terrain, will give the best results.
YES, ANY different links will change the geometry. They won't change the stiffness of the spring or action of the shock itself. It does change the linkage curve, however. Since it also affects seat hieght and is cheaper than having travel limiting spacers installed, people flock to them.
That Honda is a great bike, but you need to decide if you think you will outgrow it performace wise and whether or not to just go ahead and get something you can grow into it instead of grow out of. Good luck with it, either way you go!