I want to collect a Militarum Tempestus army inspired by the Colonial Marines from Aliens, which means conversions

I don't want to hear that's it's not competitive and is going to lose every game blah blah. I've heard it all before and I don't care. However, I would like to hear from players that have experience playing Militarum Tempestus and how things could be tweaked and optimised. I'm going for cool factor while maintaining a measure of playability. Thanks in advance.
MILITARUM TEMPESTUS - COMBINED ARMS DETACHMENT
HQ: Militarum Tempestus Command Squad (145 Points)
Bolt Pistol - Power Sword - Medic - 3x Plasma Gun
Rides in the Valkyrie with the Lord Commissar (army Warlord).
TROOPS: Militarum Tempestus Scions (150 Points)
10x Scions: Bolt Pistol - 2x Hot-Shot Volley
TROOPS: Militarum Tempestus Scions (150 Points)
10x Scions: Bolt Pistol - 2x Hot-Shot Volley
These two units are a fire-base/skirmishers of sorts.
TROOPS: Militarum Tempestus Scions (70 Points)
5x Scions: Bolt Pistol - Hot-Shot Lasguns
TROOPS: Militarum Tempestus Scions (70 Points)
5x Scions: Bolt Pistol - Hot-Shot Lasguns
These two units hide in the Vendettas for late game objective grabbing.
ASTRA MILITARUM - EMPEROR'S SPEAR AERIAL COMPANY
FAST ATTACK: Vendetta (170 Points)
FAST ATTACK: Vendetta (170 Points)
FAST ATTACK: Valkyrie (135 Points)
Multi-Laser - Multiple Rocket Pods
MILITARUM TEMPESTUS - FORMATION DETACHMENT - HELLRAIN BRIGADE
HQ: Lord Commissar (90 Points)
Bolt Pistol - Power Sword - Carapace Armour - Melta Bombs
HQ: Militarum Tempestus Command Squad (245 Points)
Bolt Pistol - Medic - 3x Plasma Gun
Taurox Prime: Taurox Missile Launcher -
TL-Autocannon
TROOPS: Militarum Tempestus Scions (90 Points)
5x Scion: Bolt Pistol - 2x Meltagun
Recycled with Brigade. Deep-striking Meltaguns that never die.