Well this is my opinion on a technician. I feel I should post becuase technician is literally my favorite class to use in Anima. Anyways, there are two ways I tend to build technicians. Technique technicians and magnus technicians. Technique technicians tend to build on a central point of technique use so i build them with the thought in mind that they won't have very high high attack and defense, but they will make up for it with their techniques and abilities down the road. Magnus technicians are quite different, in that, a magnus technician will focus on attack defense and ki abilities while carrying out little effort regarding techniques. This is a bit balanced out because once they start taking their magni they will halt their attack and defense progression.
As for martial arts that is a touchy one. Tai chi is really good if you plan to fight unarmed as it makes use of power, which in my opinion is a very good stat to have for a technician, and it also increases your MK total which is also great. But it looses meaning if you plan to fight using a weapon. If you plan to use a weapon Tae Kwon Do is a very sound way to go as it gives you that additional attack to use. There are also other sound decisions, there are almost limitless concepts when it comes to technique technicians because they can do nearly anything. You can easily make a grappling character who uses techniques to amplify the brutality of his full attack blows. or you could make a kempo character who uses techniques to unleash a gatling gun worth of attacks in a short period to devastate defenses. In my honest opinion there are many MANY ways to build a technician, it is probably the most versitile class in the game (excluding the obvious freelancer).
As for Ki techniques they are daunting at first. I suggest using the ki technique thread here on the forums to test trees. The good people here will help you work out the bugs and make the techniques viable. Everything is honed with practice and building techniques is no exception. As for pulling from multiple trees......... That can be troublesome as different trees are built with completely different mentalities in mind. There are also limiting factors such as if a technique tree uses elemental binding. Because if that is the case all techniques in the tree that follow it must take that disadvantage as well, this alone could cuase problems. Another issue is the Ki cost spread, chances are you will not have amazing accumulations at first, this is a given, and if you spread yourself to thin you may find yourself lacking late game. If you are making a technician for the first time i suggest focusing on 2-3 ki related stats to base your techniques off of. These will be the basis of what you increase when you spend DP. Personaly I urge you to try and make techniques for yourself, as VoidCabbage stated before building them is incredibly fun. You just have to be willing to familiarize yourself with them.
As for ki abilities I feel I must urge this. ZEN is not an immediate must. I would suggest taking zen around level 9 or 10. Inhumanity is understandable at earlier levels but Zen is pushing it a bit far. Presence extrusion and Aura extension are really good picks so that you can damage those pesky spirits and bypass those damage barriers. Energy armor is good, but so is absorption of energy.... considering you can just anull energy damage, that are not physical of course. It is all based on how you like to play.
I hope that this helped and I hope it is not so wordy that I scare you off. You can PM me or just reply to this post if you have any questions me or any of the other good people on this forum are sure to help. Cheers~