Hair styling gels and 'liquid gels' - effect of formulation / composition on viscosity and performance
Question 1: Carbomer
Question 2: Not sure about the question, but anyway. Sure you can create a spray (theoretically), but the process is really hard (please, do not make it at your house) because you need a propellant. By the way, such a high concentration of Parfum.
Question 3:
Part1:
According to your observations, in my own opinion, the concentration of these components maybe are too high: Octylacrylamide/Acrylates/Butylaminoethyl Methacrylate Copolymer, Niacinamide, Hydroxyisohexyl 3-Cyclohexene Carboxaldehyde.
Part2:
Maybe because of the oxidation of hexyl cinnamaldehyde to Cinnamic acid you can feel a very unpleasant smell. But it is hard to tell because everything you describe is not in a detail (for example, the scent, what reminds and etc..)
Part3:
VP/VA Copolymer, PVP makes your hair shiny and not sticky.
Panthenol makes your hair not dry.
JUST A REMAINDER:
It does not mean, that those components which I have mentioned are very good or very toxic. It all depends on concentration and experimental data. We use poisons' as drugs, but lethal and effective concentrations differ.
I answered what could possibly be in my own subjective, but a trained opinion based on your poor objective/experimental data. Try to say more about what you smell, what you feel, and there many databases of components like (found some reliable databases for you):
Official Cosmetics ingredients review database: https://www.cir-safety.org/ingredients
Cosmetics and their function (easy to use database): https://www.cir-safety.org/ingredients https://www.ewg.org/skindeep/
Chemical compounds database: https://pubchem.ncbi.nlm.nih.gov/