Well, in my opinion, (to answer your first question) it really is up to your ability in terms of memorisation - some people are great at it, others (like me) not so much. If you know you like the subjects, and believe that you are capable, then I'd say go for it!
I am in a similar position to you - still doing igcse exams, and have chosen my IB subjects, so I haven't had any experience in IB yet (sorry about that), though I've heard quite a lot!
I originally chose both languages at A as well, but dropped down to Chinese B (HL). Once again, I think it depends on your ability for languages. Even though chinese is my mother tongue, I'm not very good at it (I'm terrible at reading and writing), and in order to do well in it I knew I'd have to spend lots of time on it, which I didn't think was ideal, as I don't need Chinese A for what I want to take in university. In my opinion, I don't think the bilingual diploma is very useful unless you're planning to pursue something related to language, translation, etc. My brother took Chinese A, and though he didn't do too well, he still got the bilingual diploma, but even then it hasn't really made much of a difference for him.
I'm afraid I can't offer much insight on IB Psychology, because I didn't take it at IGCSE or choose it for IB - sorry! :P Then again, to answer your last question, nothing is really easy in IB, so as long as you put your mind to something and commit and don't leave everything to the last minute, you will be capable of doing well
Hope I helped!