knowing what i know,
then i would learn some aspects of plastering because it will compliment your tiling.
my dad was what you call a real old style time served tiler and he could float out walls and swimming pools perfectly in sand and cement. he also was a taught to do floor screeds, to falls, etc. he learned to skim in no time at all. he was a terrazzo layer and served a 7 year apprenticeship in italy. he did stone work, restoration work in turin, naples and rome. there wasnt one aspect of tiling he didnt cover and he was as good a plasterer as you will find due to his tiling trade.
he claimed that if you where a tiler, then you would have far greater appreciation to why a floor or wall needs to be totally flat, therefore it made you a better plasterer than a plasterer, if you know what i mean!!!
unfortunately for me, my dad liked tiling more than kids so i didnt see him much lol
i dont always think its best to too many things because you end up slower than a pro and your real money will come from what you are good at, which on this forum is tiling. yes, be in position to floor screed and flatten/level a wall or maybe skim a bathroom ceiling but, for the rest, sub out and put some money on top and put your real skills into the meterage and quality of laying tiles ;0)