Actually, tax–saving by investing in ELSS funds depends on your tax bracket. Under Section (U/s) 80C you are eligible to invest upto Rs 1,50,000/- per annum for tax saving. If you are in the higher tax bracket of 30%, then you can save maximum upto Rs 46,800/-.
Yes, you can. SIP in ELSSS funds is similar to SIP in any other mutual fund schemes
You can invest more than the prescribed limit u/s 80C. But you are eligible to take tax advantage only for Rs 1,50,000/- and not more than that.