DIVI expert: Technicalities + Mobile optimisation

DIVI Technical help required to tweak and optimise my site across all devices. Most of this has already been done - I mainly need the Homepage header banner fixed. It's a very small website, with only 4 short pages.

Requests:
1. Contact form does not send emails to my email
2. Optimisation of Mobile header banner - to work across all sized devices
3. General optimisation of mobile phone site, and spacing issues. This is almost finished - just needs final adjustments.
4. Showing me how to make my own future changes on mobile view, without affecting desktop view
5. Check Security of site

website: www.soulalchemy.co.uk