Ok normally I dislike this kind of thread because it takes a lot of time and effort to contribute, but hey, what the heck.
My thoughts on a list to be (not tournament competitive) able to have a fun game:
Build a list with a strong purpose oriented setup.
A defensive element to hold ground in your home turf and keep those objectives smothers.
An aggressive element to push forward, hunt forward objectives or topple a flank relying overly on a melta-able lynchpin.
A 'cavalry' element to ride in and save the day when things look grim at any particular point.
I don't know your gaming meta, so here's a fairly 'take all comers-but-especially-mechanised-lists' set up.
HQ - Coy HQ with Straken, (I remember you saying you had a Master of Ordinance and Astropath, but don't see them here?), Missile launcher, carapace armour, medic, chimera.
Ministorum priest to bolster a block.
Vet Squad with Harker, 3x Flamers, Missile Launcher, Chimera
2 x Vet Squad with 3x Melta, Missile launcher, Chimera
Infantry Platoon with:
PCS with Autocannon, vox.
4x Infantry squads, each with a lascannon, flamer if points allow, to sit at the back with the priest and hold objectives as one big combined squad or similar as the board and opponent dictates.
2 x Special weapon squads, one with 3x plasma, one with 3x flamer to ride in vendettas and kill terminators or hordes. Drop one or the other if tailoring for opponent to make space for other stuff.
Manticore - bubble wrap with your infantry or hide him on an objective to fire indirect.
Light infantry hold ground and should be able to hurt monsters and tanks with that many lascannons, Mechanised troops push forward to take objectives or slay monsters and small deathstars with bulk melta, Harker pushes forward into terrain to piss off an enemy by holding ground ahead of your light infantry, vendettas kill aircraft and tanks and drop the special weapon squads where required, and the manticore sits back and shoots.