If you are going to end up mostly using psi, it would be worth considering the OSA training to begin the game. The skills you get from starting as OSA aren't the best, but the big draw is getting the first two tiers of psi for free. The cyber module cost to get tier 1 of hacking and standard weapons 1 is easily attainable in the first level, and by starting with two tiers in psi you have a lot of flexibility with which psi skills you can utilize early without having to invest too many modules. It also opens up the access to upper tiers sooner.
The other route to go would be starting as Navy. You can get the standard weapons and hacking skill for free, plus a few other useful stats and abilities: cyber-affinity for your hacking would be very nice, but maintenance, endurance and agility are also good options. Even research can be nice for researching organs without the need of the lab assistant implant.
So, the choice really depends on what you're planning to do with this character. If you are thinking of having him be an awesome hacker with a gun who then becomes a psi-master, I would go with the OSA tours of duty. If you are thinking more of being a versatile tech-psi hybrid character, who utilizes psi to enhance your overall skillset, rather than relying on it to be your main weapon, I would go with the Navy.
The next big decisions are going to be where you want to take your character. Tier 5 psi is a HUGE investment of modules, so if you want to get to the tier 5 abilities, expect to make some concessions in other skill and stat areas. Are you planning on the pistol being the only weapon you really use (aside from psi)? Then don't worry about increasing your standard weapons ability unless you find you have spare modules to spend. Do you want to use anti-entropic field rather than maintenance? Most of the specific advice would really depend on your answers to these types of questions.
However, a few general suggestions:
- Get psychogenic cyber affinity (boosts your cyber affinity stat by 2 for a really long time).
- The pharmo-friendly OS upgrade is great for a psi-focused character.
- Sacrificing tech and weapon abilities to focus on psi will allow you to boost your stats quite a bit.
-> I'd recommend high agility and endurance.
- Plan ahead and make sure to understand a psi ability's usefulness to your character before purchasing it.
-> for example, Electron Cascade is one of the most valuable psi abilities available... unless the only powered items you're using are implants, then it's only occasionally useful.
Hope this helps!