1. Power cuts can be a issue because when we mine, we get the reward after completing a block. The less amount of block you mine, the less reward you get. So power cuts can be a disadvantage. But still, winter might be okay for you, but given your summer situation, it can be a big deal.
2. I live in Mumbai and provide rigs to people nearby. And as far as my knowledge goes, the RX 400 series has stopped coming here. Only way here is if someone has very old stock, or if you go for used 400 series.
3. With your budget, their are two ways to go for:
a. Build a high end less quantity build, like 6 * Vega Series, but they are hard to get. Focus on this if you plan to mine Cryptonight's like Monero(XMR) and others.
b. Build a mid end more quantity build, like 8/10/12 (depending on what price you get) RX 570/580. Focus on this if you plan to mine Ethash's like Ethereum(ETH) and others.
NOTE: Ethereum is rumoured to shift to Proof of Stake (Google it). So plan accordingly. But if you still decide to go for it, prefer 8GB Cards for Ethereum mining for future proofing (Because Ethereum DAG file is about to reach 4GB).
Hope this gives some help to you. If anyone thinks I made some mistakes in my points, please correct me. I am no expert in this.
And just for reference, do check my website where I give pricing of rigs in Mumbai.
http://www.cryptominingrig.inHave a nice day.