You can seal your hair after washing even if you've not used any leave in products, because part of what you're sealing in is the water/moisture that entered your hair as you washing, or at least slowing down the rate of that moisture being released. I don't know whether sealing before or after gel is better - some people seem to seal last but most seem to seal before styling products (gel, cream). You could do leave in, oil to seal, styler - or reverse the first two, or miss out stages in that depending on your routine.

Re humectants in gel, I don't think that should be a big problem with the Uk weather in the next few months, although this is Uk weather we're talking about, who knows what will happen! It is partly trial and error, the Umberto Giannini gel in Boots in the pink packaging comes in a tester size so might be worth a try.
UK based wavy

Mostly waves, but curls and straight bits too!
Fine to medium, high porosity, medium density, very low elasticity
Highlights damage (growing it out), seems to like protein and need lots of moisture.

Cleanse - CJDF, trying out low poos ; Co wash- Uk chemist brands, Urtekram Rose or Aloe, Hairveda Amala Cream Rinse; RO - varies, Tigi Moisture Maniac, Desert Essence Coconut ; Leave in - Keracare natural textures; Sealant - argan oil
Trying out new things, still looking.