ninagruenewald Sorry, Nina, I only saw this post now.
The Paid membership is very useful at the beginning because you will more easily get clients by answering to job postings or consulting the Blue Board to identify which agencies to target. In time, as you gather experience and develop your marketing strategies, you may depend less on platforms such as Proz. As a paying member you get notified of new postings instantly, do not have to pay anything to answer, can read entries in the Blue Board, can access a library of free webinars on possibly any translation-related topic... you also get freebies every once in a while ? A couple of months ago it was a free license for Baccs, which is an accounting software specific for translators, and some time back free glossaries... Imho the Plus membership is worth it. If you decide to pay for membership you may as well choose the Plus plan!
As regards the second question, it's a much broader topic that cannot be answered in a paragraph, so I suggest opening a brand new discussion ? This actually applies to any other question you may have (do ask them!), it's always best to open a new topic ? The more, the merrier!