1. The left shako are for 'Northern Dutch' units, the right were for 'Southern Dutch' (Belgian) units. Why they decided use different shakos I never really found out. Some form of regimental or national pride, maybe. They abolished the difference with the introduction of new shakos in 1817.
The 35th and 36th batallions were Belgian light infantry, the 16th, 18th and 27th were Dutch.
2. Any type of regular short haircut without shaved sides would be good, really. Plenty of modern haircuts work. For spectacles, something like this
Though keep in mind that spectacles obviously were pretty expensive and not really for low-class citizens (which soldiers, by definition, were). I know a few people who wear glasses in normal life but don't during re-enactment (either wearing lences or nothing at all) but obviously they have 'weak' glasses. Kudos to you for actually thinking about getting proper glasses, it's crazy and extremely annoying how many people just don't bother.