Ave with a model o

I'd get Lian Li PC-O11DW and 650w with  tier 3 above . I personally would get RMx/WhisperM depending on the price on your location compare to thier competition. 

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 Budget , rebate btw.

450w is enough as long as theyre an ok unit , i'd care more about the psu quality at that point. you said rs so i assume you can get this https://www.amazon.in/Corsair-CP-9020120-NA-CX450-Power-Supply/dp/B01MTZ96RU/ref=sr_1_1?ie=UTF8&qid=1540199104&sr=8-1&keywords=cx%2B450w&th=1. 

which platinum? if you get Focus series I'd rather go ahead and get something like Whisper M instead. here a review about taht

https://www.hardocp.com/article/2017/10/24/seasonic_focus_plus_gold_platinum_750w_review/10 

I'd get Lian Li PC-O11D and this psu if i was you . https://pcpartpicker.com/product/2HbwrH/corsair-rmx-2018-650w-80-gold-certified-fully-modular-atx-power-supply-cp-9020178-na