The 3rd strt raise has the potential to knock out one or more of the following players: 7,8(the bring in),2, 3, 5. It is not known how many would drop out with the raise, but the bring in is likely and anyone with an upcard lower than the jack.

In stud, if an aggresive situation presents itself, take it if it looks reasonable. And in stud, if a situation presents itself to knock out 1 or more players, take it if it looks reasonable.

As for 6th, you are right what you say. I meant to say, just bet it outright and not check. check raising does not look correct there.