Help me improve website

Description

Please see our website here: themodelclub.co.uk
Background:We used a freelancer to create our website and the backend of our website (where we can control the models on the website, along with the applications we receive through the website) however - we can no longer get hold of her, and we need someone to step inI have the backup file
There are a few things we need help with:
- The website is very slow! We need help to speed it up- I love the design of the website, but something is making it flat - we need to make it more elevated- We are having problems accessing applications through the backend, we will need this looked into- We need to market our website using SEO
Please let me know what you can help with, and show me examples or tell me how you can improve our website. I do not want to see generic portfolios that are not related to our website