Just finished IB. It's great and honestly not as "hardcore" or whatever as people make it out to be, you just have to manage your time. Out of the classes you're interested in, I took HL bio, HL psych, and English A. What people find easy or hard is super subjective in my opinion, other than the commonly held view that ESS and maths studies are some of the easiest classes, sort of soft options in IB... I would definitely agree with this on maths studies, but I didn't take ESS so I don't know about that.
The sheer volume of stuff in Biology was daunting. It's not challenging to understand the concepts, in my opinion, but there's just so much stuff to learn! If you keep yourself on track though, it's doable and very interesting. Biology was one of my favourite classes. I would say there was more theory taught than practicals, which I enjoyed because I don't like practicals too much :P
Psych is a very interesting class. I had a **** teacher, but if it was with anyone else it could have been really great. Basically, there are 3 core units; biological, cognitive and socio-cultural. You learn the principles of these "lenses" through which to study psychology, and case studies which fit into each topic, and overlap. It was actually nice to take biology with psychology because in the biological unit, some things overlap like learning about neurotransmitters and stuff. Then you get to pick two optional units for psych; most classes pick abnormal, where you learn about mental health disorders, and my class also picked health psychology, where you learn about addiction and health promotion. Pretty much in psych you're just learning about case studies and applying them to the learning outcomes of the course to construct your own ideas about, for example, how reliable the cognitive process of memory is, for example. It's very interesting, and for the internal assessment you get to replicate a real psychological experiment. I highly recommend taking it, and it'll be useful in a lot of areas.
About SL maths - I'll just say I found it quite hard. I was in it for a few months at the beginning of IB, but I've never been great and maths, and knew I didn't want to go into a scientific field, so I switched to studies. Studies is very low level; it was too easy, and SL was a big jump in difficulty for me - in my opinion the IB needs a course in between, but maybe I'm just really bad at maths haha.
Also, taking a non-ab initio language is ambitious! In most classes you're meant to go in knowing the language, almost being fluent; just a word of warning.
English A is obviously the bomb dot com I won't even talk about it, you know it's gon' be great. Especially if you have a wonderful teacher. The stressful part of this class, for me at least, was the individual oral commentary - where you have to go in with the teacher, and give a 10 min commentary on something that you have studied, but you don't know which one will come up on the day.