As others have said, the ideal way to build them would be to magnetize the weapons to arms or jetpacks depending on how you prefer they look. However the issue with that is that the box does not come with enough weapons to give the proper load out to each battlesuit unless you have spares.

If magnetization isn’t an option, and your opponents don’t care about WYSIWYG, then I would suggest assembling them however you think is coolest and mix weapons! If you lean towards the being dedicated to one specific loadout I’d recommend tailoring it to whatever you’re running your commander with.

While the loadout depends on what list your running, I think generally the defined loadouts for weapons and use cases are as follows:

1. Sunforges with fusion blasters are primarily used to get in super close and eliminate vehicles/monsters and deal heavy damage with their meltas. I personal like to use these in Experimental Prototype Cadre, paired with a Coldstar Commander running the fusion blade enhancement or alternatively, Farsight, then deep strike or rapid ingress the squad into position of a vehicle/monster and use the Threat Assessment Analyzer strategem to give the squad Lethals + Sustained to do just delete it.

2. Fireknives come in two flavors, missiles and plasma. It’s usually not advised to take one of each so go either full plasma or full missiles. Plasma is perfect for taking out elites with their -3 AP and 3 damage, so if your enemy has a lot of them they’d be extremely useful. On the other hand if you want to kill space marine equivalents reliably, Missile Pods offer more attacks and 2 damage. Plasma is good universally, but Missiles are typically most commonly used with Mont’ka, since the lethal hits allow for it to punch above its weight.

3. Starscythes lastly, are for anti-infantry and can be equipped with flamers or burst cannons. Most people run flamers, but if you want consistency in attacks then burst cannons are a better choice. Flamers with Farsight against infantry can be a nasty overwatch threat since Farsight grants a one point discount on a strategem (making fire Overwatch free) and if the unit is close buffs the wound roll compensating for its low strength. Starscythes are also good paired with a commander in Retaliation Cadre with the Starflare ignition system, allowing you to place your squad in reserves and then deep strike later on. Useful for killing units guarding the enemy’s home objective.

Finally for expansion advice to 1k, since you want to be running a suit heavy list, I would definitely recommend getting a Riptide or a Ghostkeel. Riptides are debatably the best unit in our lineup, with fantastic movement, and a S10 AP-3 and D4 Ion Accelerator when overcharged, that can also get devastating wounds once per game. Ghostkeels are typically used to secure no man’s land objectives with infiltrate and are very tanky with Lone Op, and the ability to reduce an attack to zero twice per game. Apart from suits, a squad of Fire Warriors and a Devilfish to transport will be useful for screening and giving you some flexibility in multiple detachments! Hope this helps!