>100 bitcoins. Will I be a millionaire by 2020?
No.
Why not? bitcoin prices are always unpredictable, as we now touched $500 in a short time. so in 2020 may be 100 bitcoin be a millionaire, if the price above $1000 No.
Bitcoin already reached $1000 highs. Remember how that shit-show turned out ?
The fundamentals are not yet there, for Bitcoin to be valued at 1BTC/$10,000USD.
I doubt the price would even go to 10.000. It's just to high if you ask me. At best the price may go to 3000/5000k but there are never guarantees.
For that matter, it's also possible the price will go back to 1 dollar if some very bad news arrive.
So better to be very carefull, it's your money after all