I thought Insanity for single player was balanced much better than ME2... except Marauder Shields... but I used my max level character for Insanity in ME2, which makes things 10x more difficult, I'm told.
I did my insanity run on soldier and even then, I remember having lots and lots of extra credits. Most gear is free and I only used a small portion of the guns.
In the end, I think I just upgraded all my guns just to "complete" things, but I found it is worth it to max the guns for your squad first if you haven't done so already. It surprised me how much more damage my squad put out (and I never rely on them for anything for some reason). I found SMGs and, surprisingly, snipers worked well for them. Assault rifles have issue with armor (ammo powers and mods help a lot though), shotguns got everyone killed, and they like body shots with pistols for some reason.
Weight reduction and spare ammo can be significant when upgrading, so there is that. Since you use your squad powers and they shoot regardless if you want or not, this allows them to use bigger weapons while keeping cool down low (and maybe taking alternative upgrade options).
For adept, personally, I'd max out a Carnifax, Paladin, or Wraith then whatever your squad uses and be done with guns. This either makes you a light weight sniper (between power uses) or a force to be reckoned with at close range (in case something sneaks up on you).
Widow or Black Widow are good too, but heavy. For teammates, the Widow is significantly better as it's higher damage, lower weight, and ammo doesn't matter to them.
You could also invest in a gun that's not meant for damage such as the falcon. It staggers most everything, which may save your *** if a phantom gets too close or prevents Cerberus from dodging your powers.
As far as what else to buy... no, there really isn't anything else (I believe).
Edited, Mar 13th 2013 3:15pm by xypin