1) Multimedia doesn't need SLi
2)SLi is used for better gaming and if you don't game then there is no point.
3)SLi is mostly a recommended solution when you are going for a relatively high end solution, eg : 7900GTX SLi, in stead of 7900GT SLi you can get 7950GX2, instead of 7600GT SLi you get 7900GT Extreme or 7900GTX
so there is only proint if you are willing to put at the very very minimum 35k or more in your graphic subsystem and recommended mainly for 60k+ solutions. however 7950GX 2 might not be available in india so you might need to consider 7900GT SLi
4)The mobo shouldn't make much difference, but may have more features, a higher mobo is likely to perform better, so you need to check that out. Also, A8N SLi Delux i think is not that good an overclocker, so no point, unless you go for something very high, in fact as such the highest then it may oc even better.
5)There is a DFI sli mobo i thik around 7500, but if you don't use sli then you are only paying for more performance(if it gives) and features, if they are there.
6) Asus A8N E is good.
7) I deserve reps for this