>Individual Carbine
>Assault Rifle
I'd go for the Valmet or one of its descendants (Galil or R4) to fill both roles. I'd do some serious testing of a 6.5/.223 or 6.8/.223 cartridge for it, to get better downrange oomph than the .223 while keeping the small form factor.
Variants with folding stocks or drum feed to work as PDWs, SMGs, or LMGs.
>Designated Marksman Rifle
I'll stay with the Kalashnikov pattern here, but step up to .308 and a scope. Militarized Valmet Hunter or Molot equivalent.
> Sniper Rifle
Heavy rifle in .50 BMG or .338 Lapua. Since I have no particular preference, I'd want to look at combat results and armory records before making a decision.
> Combat Pistol
I have some rather specific views of the role of a pistol in combat, and they don't involve being a bullet hose. Model 1911 in .45 Super or your choice of double action revolver in .44 Magnum.
Discerning readers may detect some AK and 1911 favoritism here...
> Phased plasma rifle in the 40-watt range.
I wouldn't trust imported dilithium crystals. Besides, Expert Gun Writers all agree you need at least 55 watts to do the job.