Well, I'm also a BCA and didn't opted for MCA as I'm not good in Maths.
I'm doing job right now along with freelancing on my free times.
I had also researched on M.Sc(CS) or M.Sc(IT) like you. The thing I got is M.Sc(CS) includes Maths but M.Sc(IT) doesn't. But I really didn't find any profit of doing that. Because after monitoring many job emails for months I rarely saw recruiters want M.Sc(CS) and M.Sc(IT). Still M.Sc(CS) has better opportunities than M.Sc(IT).
Yes like me you can go for International Certifications along with Job. That experience will really going to matter later.
So I'm now arranging money, but didn't started anything yet.
So for the field of security, and computer networks, I'd say consider CCNA, CCNP, CISSE, RHCE, RHCSS, CEH.
I'm interested in security too but more interested in Programming, Now as I choosed my domain, I don't want to change it. Though I'm planning for RHCE. Will consider RHCSS, CEH etc. if I can arrange money(which I think I can't

).
One more thing, these certifications helps getting promotion rather than job mainly. I'm not saying that you won't get job with these certifications, but promotions are mainly considered based on these certifications(I may be wrong, please correct me if I'm wrong).
As you said that you are interested in Java too, you can consider learning J2EE to increase your knowledge from just J2SE that was taught in BCA. Consider Java Certifications too, like SCJP, SCWP etc. if you are interested in programming more.