Is it worth splitting off some of the smaller ones for replanting now, or should I wait a while?

scuppeteer wrote:If you leave them until end of April, then as boingy suggests pick the strongest 3 or 4 bines and pull out the rest, if you end up with a bit of root on the ones you have pulled off stick them in another pot, otherwise discard them. Should you wish to you can continue to pull off new shoots until July to encourage stronger growth of the main bines.
Your pot size is fine, as in a real hop garden distance between hills is generally 6-8ft, and the roots do need some room to grow once established.
Don't let the soil dry out too much in the pot when the summer eventually comes, you will notice the leaves start to curl if they are thirsty. I often water mine daily in the height of summer. It won't hurt to cut away last years bine which I can see in your picture. This will leave them less susceptible (is that how you spell it?) to disease and downy mildew.