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It sounds like you have little or no steem at present.
My view would be to weigh heavy on steem, less so on BTC.
So, that would mean buy 8k steem, and keep 1 BTC maybe.

Diversify. Don't put all of you eggs in one basket. Also, if you invest in steemit, make sure you put it into Steem Power!

What's the difference between the different steem currencies?

I would put 15-25% of that in Steem, keep the rest in BTC and possibly ETH. Diversify. Cryptos fluctuate like crazy so your best policy is to spread your risk