To your first question - how often is optimization of customer journey taken up? In my experience, very often. I am the PM for returns, refunds, and logistics. That requires me to constantly think about better customer experience. Such as, what should I do so that the customer has faster delivery? Items delivered in 3 days, 2 days, 1 days, infact sometimes within hours!! All of this without hampering any customer experience and ensuring quality service because some of these brands are extremely high-end serving celebrities. Not to say that other customers are not equally important. The point I'm trynna make is you will be constantly thinking on your feet.
To your other question, B2B may or may not require heavy UX. Depends on your role and scope of project. But if it does, you have got ample of methods. A/B test tops the list. Since you are just starting out, I think A/B tests will help you make correct data drive decisions.
Wish you luck!!