There's only one weapon combination available, but it's the only one you'll need. The Multi-HMG provide long-range, high burst, heavy hitting firepower to deal with everything from basic line troops to the strongest TAGs; and the heavy flamethrower provides a close-in ARO threat for anyone that thinks getting close will help.
Additionally, it has an AP CCW at Phys 17 which can do an enormous amount of damage if it hits (a bit if). Don't rely on it, but keep it in mind in case something ends up in base-to-base with you despite your best efforts. Given your armor and structure points though, it's preferable to drop the heavy flamethrower on someone charging you instead of thinking CC will solve your problems.
Thanks to Fatality the Multi-HMG (but not the Heavy Flamethrower!) is damage 16. It's a suitably scary weapon for the most advanced TAG in the Human arsenal.
The Marut lacks any defensive mods, and instead relies on heavy armor and high BTS to protect it from failed rolls. Against things like Explosive, Viral, and Plasma this can be a major problem; especially when paired with AP/Breaker ammo types. Protect yourself by staying in cover and targeting as few units at a time as possible. Tactics are your friend, because you're walking around with a TAG more expensive than all but 1 (the Avatar), and none of the fancier niche tricks that many of them can pull off.
One thing that is going in your favor is your MSV2. You're ignore regular smoke, camouflage mods, and mimetism/ODD. At BS15, you're even able to take decent shots at enemies in cover. Still, fall back on this as a secondary measure instead of a primary plan.
The Marut is the hard counter (or as much as there is one) to the Avatar. With MSV2, a Multi-HMG, and no cube (so it can't be sepsitored), it is happy hunting down the EI's most dangerous beast. Beware though, the Marut is still vulnerable to hacking and possession.
The Marut is expensive and is best at range. Getting up close with mono-filament weapons, or shooting it with AP+Explosive weapons, preferably with Surprise Shot, will be the best way to take it down.
Better though is to either try and hack it to immobilize/isolate it, or kill all of its order generators. Aleph is expensive to begin with, and bringing a Marut will limit your opponent's ability to bring top-tier backup plans.
The Marut is your most valuable (and expensive) asset, even more so than a typical TAG list. It should be your Lt. for the Stragetos lvl3 perk and because chain of command is so easy to get. Next up, you'll need either the Myrmidon Officer (if playing Vanilla) or the Shukra Consultant (if playing OSS). Myrmidon provides valuable smoke, and the Shukra can hunt down impersonators that are threatening the Marut during the first turn of the game.
After that, you'll want a set of Proxies (at least one of which should be the engineer), a Netrod for the cheap order and to protect the Proxy's order, and some kind of midfield skirmisher. Season the rest of the list to taste, though you'll be fairly limited in what you can bring along points-wise.
It's best to leave ARO duties to units like the Proxy multi-sniper, but the Marut's Explosive ARO shot can be useful if placed in a limited fire lane. Have the engineer nearby if you plan to place it on ARO duty though, because there are several units that will be a threat. Alternatively, set up in total cover with the help of Strategos lvl3, and come rampaging out during your turn.
Active Turn Role
Shoot anything that looks at you funny. The Marut is Aleph's blunt instrument, and excels in that role.
Damage 16 Explosive ammo at BS15 and a heavy flamethrower mean the Marut is dangerous at most ranges. Keeping the Marut back and putting it into suppressive fire watching an objective is also effective. Either your opponent will need to avoid the area, or bring in a long-range trooper/hacker to try and drop you out of your suppressive state.
Just remember that your Marut is a vital element of your list, and risking it unnecessarily might cripple your ability to keep fighting.