Allocations should be based on your overall risk tolerance, I can't really guide you to that. When I first bought Bitcoin, I did so with an allocation I was completely comfortable with going to $0. You also have to do so with an allocation you are comfortable seeing 50,60,70% drawdowns on, because eventually it will happen. I have recouped my initial investment in my Bitcoin and then some, so for now I'm kind of riding the wave and this is why you see me with higher allocations.
For ETF vs owning outright, I prefer the ETF due to the tax sheltering capability. Gurgelph is right in the fact that if you don't have the keys, they technically aren't your coins. So a lot of hardcore Bitcoiners refuse to own anything but Bitcoin outright. But, I trust iShares in regards to IBIT, the coins are in trust, and I'm happy just owning that.