Most important question: Will you have access to a hacker to supplement your abilities? If you do, then the hacker can perform the non-essential matrix activities (locating nodes, data search, tracing, fighting on the matrix), freeing you up to do the truly dice pool intensive activities (hacking, spoofing, disarming, stealthing). One of the huge TM advantages is getting a ridiculous dice pool in a few actions, so you should figure out your actions and specialize.
2nd question: Determine what your fade stat will be, and if you plan to be a “I stay in the van” style TM, or “I go into the hot zone with the infiltration team” style TM, because they are very different.
The following information is assuming you have a hacker, and you stay in a van.
On complex forms:
It is much cheaper to buy complex forms with BP and expensive to buy them up with karma (plus it can be impossible without good intuition). Sit down with your GM and learn how the matrix works. Each GM runs the matrix slightly differently and it is important to know how yours will run it.
Buy the “critical” complex forms up to your resonance (either 5 or 6). The “critical” ones to me are: Exploits, Stealth, Spoof, Command, Disarm, Analyze. Basically if you want to be a hacking TM, you should focus on the things with opposed rolls.
On skills:
If you want to hack, get hacking at 6. The rest of the cracking group is meh (cyber combat is bad, and electronic warfare is only worth it for decrypt or if you don’t have a hacker).
The Electronics skill group is great and you should have it at 4.
The technomancer skill group is bad, as decompile is not useful. There are better ways to fight sprites (which you will see extremely rarely in my experience). Registering is good, Compiling is good. Note that you are usually Fade limited on how much you can thread or how big a sprite you can compile, so do not feel like you need huge compile or thread pools.
On Fade:
Getting Fade Resistance has clear diminishing returns after about 10 or 11. You can get higher (15-16), but it might not be worth it, you give up a great deal of BP for it. Remember that you can both First Aid, and Heal Fade damage, as it is not magical. Use this to your advantage.
On meat-world:
Get a drone. Install a rigger cocoon. Sit in that, and remote control the drone using a really high Command complex form.
On Cyberware:
I have determined one good cybered/TM build, but unless you plan to use it, stay away from cyberware.