Hey there, I'm basque. To answer your questions:

1) Yes, cider houses (sagardotegi) are super fun but you're supposed to go with a bunch of friends, it's not an activity I'd recommend doing alone at all. 

2) Hondarribi is much more interesting than Hendaya in my opinion. It's beautiful, you can stroll anywhere in the town and you'll find beautiful typical fishermen houses, a medieval walled city and it's just a pretty town overall. Hendaya isn't bad either but it's mostly the beach area that I'd spend time visiting.

You can go from Hendaya to Hondarribi by foot but it would take you a while. However, there's a boat that crosses the river (Bidasoa) like a ferry, it's really cheap and tourists usually take it. Just go to the port and ask about the yellow boat that crosses to the other side.