Your best game plan here seems to be priming him in.

10/9 6/4 5/4

6/4 5/4 is clear. I prefer 10/9 over 12/11 because you want to keep a spare on your best blocking point to diversify your prime making numbers. Hes got too many blots on his side of the board so you'll probably get the best out of a hitting contest if all goes wrong.

Cheers.

Agreed. Make the 4-point and then play 10/9 to make either the 7-point or the 8-point next turn. You need those points to keep White contained and to make it easier to clear the 9-point later. White won't hit unless he rolls 4-4. All other hits are too dangerous.

Has 10/8 (2) some merit to make the 8-pt right now? Or is the 4-pt a clear-cut must?

Making the 4 is mandatory, it's the last ace that you have to worry about.