I meant if you look at the Part IB papers, you'll see that half the questions are are on topics learnt in 1st/2nd year: thermodynamics, stat mech, quantum, liquids and solutions, spectroscopy etc for physical, ditto for inorganic and organic. The 3rd year material only makes up half the papers!
Tbh I was very lackluster with past papers since I left revision quite late and I needed to go over content first
But if you do start early, then definitely do all the past papers, you'll feel so much more confident. I looked at some older papers instead of sticking to just Part IB but only if I was sure that the entire question could be done with just required Part IB knowledge. The syllabus has changed quite a bit so there may be bits that we don't know in the older papers
It's most useful to use the older papers for inorganic paper II, which is the essay paper. Make sure you start practicing writing essays early as well!
Not all the first year material is required, just specific parts. I also couldn't do the first year physics/mechanics and never did learn how to
I don't recall much of it coming up in physical paper but I didn't do very well in those so I'm not the best person to ask
For options, it depends on where your strengths lie. Almost everyone does inorganic molecular spectroscopy because so much of it is similar to what you've done in the inorganic lectures already. Go to the lectures for this even if you don't do the option, it will help for the inorganic papers.
I did Functional Organic polymers and Natural Product Chemistry. I quite liked Natural product chem since it mostly required memorisation of the reactions, but I've heard the inorganic ones are quite good because it again requires lots (massive amounts) of rote learning but otherwise the questions are simple.
I'll PM you which labs I've done/recommend