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/This is the most easiest way when it comes on transacting or even buying on bulks but talking about the rates then expect it would really be more higher compared into the market price 10-15% in my own experience but somehow there are other sellers that do rush selling if youre lucky enough to catch it then it would really be worth.