Not a beginner, Capital isn't a problem, I run a crypto based business and am always looking for sources to buy large amounts of coin at good rates.
I'd say probably Localbitcoins[1], as you wouldn't have problems with banks and taxes and stuff because you can purchase peer to peer, even with physical cash. Though I'm not sure if you can call it "good rates" though. I suggest posting your own offer for optimal rates.
[1]
https://localbitcoins.com/Localbitcoins price usualy depends on the current mood of the traders in your location. In my city you can always buy crypto for +15-20% over the coinmarketcap price and sell for -10%. OP might try to pick some safe and popular payment methods get some trades on localbitcoins for better trust and then place his buying ad. As I remember he will need about 0.1-0.2 BTC to make this ad visable on the website but a chance to buy crypto below the market price might worth it.
Purchases with higher benefits are usually connected with higher risks (like buying / selling via Paypal etc.).