I'm not sure to understand.
Are you offering a life-time 400$/week after the 100BTC loan is repayed ? (in BTC?)

So if I loan 100 BTC to you today, the following happens:
- in 40 days, you begin paying 400$ per week
- in 6 months, you repay 100BTC
- in 6 months, I got my full 100BTC back and a life-time payment of 400$/week

Did I get this right?

Of course, I also considered the other options which included you repaying a loan of 100BTC at a rate of 400$/week, but that clearly does not fit in a 6 months timeframe.
Not mentionning holding the 100 BTC would be so much more profitable than lending to you, at the current growth rate.