Boost is probably the most important action a "Warthog" can take, as its dial is sub-par at best, and suddenly needs to keep things in arc.
Engine Upgrade doesn't interfere with any of your suggestions. However, it does cost 4 points.
R7-T1 is unique, but also gives a target-lock, albeit only one on an enemy at Range 1-2 who has you in their firing arc. Taking it costs one less, but removes the possibility of an EPT-based double-buff.
You also forgot an upgrade that provides a double-buff, with good synergy on "Dutch"
R5-K6 is a worse Fire-Control System, sure. However, it gives you the possibility of passing out up to 3 target-locks from Dutch, freeing up his action economy for focusing/boosting, and still providing the double-buff for which you are looking.
Only problem is that it isn't a guarantee.
However, the BTL-A4 does provide the ability to chain each success into another attempt, in a single round, and that can be awesome.
It should also be said that offensive actions suffer from diminishing returns. A Focus or a Target Lock will both, individually, increase your expected damage by 25% of the dice you're rolling, but if you already have one, taking the latter will only improve your odds by 18.75%.
Spreading them over multiple attacks, however, mitigates this.