@Ashwin

Regarding long post, its not a issue. You should write as much details as you want and it helps in answering too.

Regarding Antivirus selection, I wont tell you what my personal favorite is but i Would suggest two options for you.

Kaspersky or ESET NOD 32.

Both are almost great in terms of performance and doesnt consume too much resources too.

If you are still not sure, you can try their trial versions and see for yourself. Both of them are good enough.

Kaspersky though is cheap if you are buying it in India.