The most sensible tax is capital gains when you sell and your profit is above a certain threshold and the bog standard VAT just like everything else if you're buying stuff with it.
And considering what India was willing to do to its population when it came to cash and gold I can't imagine it's going to flourish for long.
As far as I understand only the receiver (or buyer of BTC in our case) pays the tax. It would be very silly if both, the buyer and the seller, were obliged to pay the tax but it is not the case imo. CMIIW.
Regarding the India's ban of crypto currencies, I have never doubted that their government will make a smart decision eventually. I'm glad they are on the right path.
Anyway, this is a positive news for the crypto exchange markets. I expected that the government of India will change their opinion. Probably, their Central Reserve Bank threatened by banning the crypto currencies in order to announce this tax politics. I guess that the tax 18% will be reduced in the future.