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First the list:

Primary
HQ MotF(Iron hands) power axe 105
Troops Tactical x10 Flamer, rhino 180
Troops Tactical x10 Flamer, rhino 180
Heavy Predator tl las/ las 140

Allies
HQ Fireblade 60
Troops Fire warriors x12 108
Elite RipTide ion, tlfb, ewo, stim 225
Heavy Skyray dpod,bsf 131

Secondary
Knight Errant 370

1499

The firewarriors and 2 HQs all hang out together in cover with the riptide, skyray, predator and Knight nearby pumping out firepower. MotF repairs the knight, pred and skyray. Tacticals (or just rhinos) stay in reserve if I go second, as there does not seem to be an easy source of firstblood otherwise. HQ repairs hullpoints on the knight and other vehicles. Everything is as tough as nails against S7 or less.

To all over the place, or crazy enough to work?

How are you taking two allied detachments with only a single primary detachment?

Knights are not an allied detachment.

They can be taken in addition to your primary and allied.

Works almost, as the MotF cannot fix vehicles outside his codex

Why not? Says "friendly vehicle". Battle brother count as friendly units.

RaW? Yes.
RAI? No Idea.
HYWPI? That varies from person to person.
Just remember that because one person perceives something one way, it doesn't mean everyone else does or that it's correct.
But it's down to your gaming group/TO. If you can convince them, go ahead.