UPCAT

Till 2016 HBTU was taking admission on the basis of UPSEE marks but after that it declared admission on the basis of JEE Mains score card only.
https://www.shiksha.com/university/harcourt-butler-technical-university-Kanpur-5040

Basically, below 450 it's not easy to get a good to college for CS branch as the demand is very high. For 168 you can try a good private college or even try UPTTI Kanpur which takes admission using UPSEE too. Even at Galgotias College, there are very a few chances of getting selected however you can get admission using Management Quota.

Yes, for SC category the cutoff is not less than 80 so you can apply for any government college.

Yes, you can try for the admission as you marks are good you may get admission in chemical engineering and it is a good career option. You will learn more things from this and this will provide you a good job.

The answer to your question is 2 times.

Yes, it is necessary.

It depends on your rank. But you are from SC from category, I think you can get admission in ABES. IMS or RKGIT
but try for all rounds of counselling until you get the best college.

There is very less chances to get in JSS but you can try in any other college or KIET. I am sure that you can get mechanical.

No, it's not necessary. Any state student can take the exam for admission.