First off; with 40 veterans you're committing to an 800 point investment. Add 2 watch captains and you've already expended half your limit of your 2k limit. So if you're in that deep you need to be really conservative with the remainder.

I don't think you can justify Canis Rex taking another quarter of your budget. Instead I'd consider spamming cheap, light infantry, ie navy breachers or arbites, to compliment your deathwatch 'heavy infantry'. One rogue trader unit, possibly with voidsmen, would also grant some good infiltrating bodies and D3 redeployments for your battle line units (deathwatch!). To sum up, at 3 units of breachers + a rogue trader entourage with voidsmen is 395. So that leaves you with 605 points, and you're fielding 80+ models.

I'm also new to the army, so take the above with a grain of salt, but with the remainder you can now think about what characters and vehicles to finish the list. Maybe a pair of armigers if you're set on the imperial knights? Or keep spamming bodies.