1. In my opinion, Bitcoin is number 1 and the most popular than any other coins. Because the history say so, at least so far. It has it down so many times but it came back stronger. So it is a difficult matter if you say that ethereum will overtake bitcoin. The popularity and the support of massive people will make bitcoin strong at the top of the chain.
2. I guess you can hold both of them. But for me, i will make a portion of what i will hold. Like bitcoin 70% and eth 30% , or maybe 80% to 20%. For me, i just hold bitcoin and change my alt coins to bitcoin when the price is right. But i suggest you do your own calculation.