You will obviously get different takes on this one especially here on this forum. Since you are planning to hold for a long time, I would say put 80% to BTC while 15% to high cap altcoins of your choice and 5% to mid caps. I have a few of them in mind but I would rather let you look into them.

If I may add, you could also play with altcoins for short term and move them back to BTC (making your port 100%). Many altcoins are performing better than bitcoin in USD value and also doing well against BTC but that trend won't last long. It could end in six months time.