Its been a while since I last played a game of Infinity (my club had good run at playing for some months early this year).
Army List generation is both simple and hard.
You must have a Lieutenant Unit to lead your group
Otherwise units have an 'availability' value to limit how many duplicate models you have.
SWC - Special Weapons Cost is capped based on size of battle, you will find that certain have a SWC cost.
Otherwise spend points on what you want.
As you said, some scenerios require certain skills or units like Hackers. I've found the game to work best when you play for the mission but you can still win by taking down 60% of opponents force.
My Example Aleph 200pts
GROUP 1 (Regular: 5/Irregular: 0):
MARUT Lieutenant (Strategos L3) MULTI HMG, Heavy Flamethrower, Nanopulser /
AP CCW. (3 | 122)
DAKINI Tacbot Combi Rifle / Electric Pulse. (13)
DAKINI Tacbot Combi Rifle / Electric Pulse. (13)
SOPHOTECT Combi Rifle, D-Charges / Pistol, Knife. (31)
YUDBOT Electric Pulse. (3)
DAKINI Tacbot Combi Rifle + Light Grenade Launcher / Electric Pulse. (1 | 18)
4 SWC | 200 Points
Marut is the Lieutenant
with Sophotect Medic\Engineer with Yudbot to run around for her
with 3 Dakini grunts
Bit of a brute force team with the Marut taking point - but hopefully this helps.
Use the website army generator than the book.
Love the models, game play and rules do take a lot of effort to learn / understand.
Actually played a game that lasted 1 turn and I didn't move a single model and lost!!!
Whereas another game lasted 2 hours where no one got killed and I won due to my Hacker downloading the information first.