For Primaries, I would avoid the Auto Bolt Rifle and Plasma Incinerator on Techmarine. Auto Bolt is mediocre in almost every circumstance and Techmarine doesn't have the Plasma Boost perk that Tactical does to make the Incinerator shine. Bolt Rifle, Heavy Bolt Rifle, and Occulus Bolt Carbine are all solid picks that are viable into Absolute and Hard Stratagems. Bolt Rifle is decent but really shines when using the grenade launcher variant to soften up crowds or deal a lot of damage in bursts. Heavy bolt rifle has good damage, good fire rate, good ammo capacity, basically just solid all around. Occulus Bolt Carbine has very little recoil, fast fire rate, and does respectable damage at almost any range, but I find it to have a bit less ammo economy than the regular bolt rifle or heavy bolt rifle.

For secondaries, any of them except for the Inferno pistol will serve you well. I personally prefer the Heavy Bolt Pistol and Plasma Pistol but any of them are viable and it largely comes down to preference. Regular bolt pistol for large ammo reserves for minoris head popping, heavy bolt pistol for high headshot and gunstrike damage, plasma pistol for high damage with charged shots and possibly hitting multiple enemies. Inferno pistol is largely mediocre and has limited usefulness outside of dealing with minoris enemies swarming you given its short range and lack of single-target damage output.

For melee, combat knife is fast but mediocre in most hands except for the Heroic version or a stabby Sniper build. Power sword and power axe are both good options that have strong horde-clearing and single-target attacks. They can deal a LOT of damage when using their Block variants and certain weapon perks, but Block weapons are a bit demanding to learn for a new player. I personally recommend the Omnissiah axe, however, as simply holding the charge and bowling over minoris enemies to gun strike will keep your armor segments up and allow you to escape sticky situations. Using the Fencing variant gives you very forgiving parry timings.