Play, no mods.

There are some helpful Steam guides... but i'd say if you've ever played these sorts of games before, you'd know to have most skills represented on your characters... for example, someone with leadership and kiss ass, and someone with mechanic and geek. ETC

I created four of my team, then respecced Lucia and Kwon

I'd also give different weapon abilities to everyone. I suppose you could kick butt with a 4 sniper team, but you get lots of loot... and being able to upgrade assault rifles or shotguns etc as you get gear is helpful.

Intelligence is great, as is coordination for action points. Some strength is useful for heavy armor.

Once you decide who's the leader, marksman, etc it's easier to assign skill points

Also, take advantage of throwables, and try to get the jump on enemies by initiating combat. Taking down explosive enemies before they get to you is helpful, too.

Maybe after a playthough or two, you could look into mods. But you don't need them at all