B.Sc

DMLT can be pursued after B.Sc in chemistry, biochemistry, microbiology or lifescience.
I personally feel that rather than doing DMLT after B.Sc, one should go for M.Sc in biochemistry or microbiology or in medical biochemistry or medical microbiology as doing this course you can still do what DMLT can do, but you also has an added advantage of go for research and other industries as this course has good scope.

Yes. In most of the institute, 3 years state polytechnic diploma is considered equivalent to 10+2 and if it is IT computer science diploma then you are also eligible for direct 2nd year admission in B.Sc IT and computer science as of now Mumbai University, Madras, Madurai Kamraj, Annamalai offer this facility.

There is no point on doing B.Tech after completing B.Sc computer science and recruiter may not take this positively. Better, you should decide to do B.Tech now only as B.Tech from a good institute has more job prospects or after B.Sc computer science you should opt MCA.

Sorry, it does not offer B.Sc in nursing course. You can refer to the college link for better understanding:
http://www.nuv.ac.in/