I require simple bug fixes for a responsive mobile wordpress theme

We have a current Wordpress responsive theme purchased from Themeforest however the developers responsible for support have disappeared and we're left with mobile views which is a bit buggy on some devices.

There seems to be some issues with the mobile/tablet views on some devices, whether it's the CSS or not I'm not sure.

I require someone to investigate, test (preferably on a HTC android, iPhone4/5 & iPad), amend and optimise the view port for mobile devices. I need someone with a good eye for detail as there will need to be CSS tweaks.

The issues are:

1. Very slow load times on mobile
2. Very slow scroll on Android devices
3. The site tends to hang/pause on load on Android too - assuming the site is making too many requests and/or downloading too much data?
4. Remove menu button at top as we want the nav to always appear below the header
5. General tidying up of content and making sure font header sizes and other page elements are displayed correctly. i.e. home page slider also seems to be hiding under the header on mobile devices
6. On inner pages, the previous developer has enabled a swipe-right to bring in the sub-nav but this interferes with browsing quite a lot and is quite frustrating so we'd like to remove this function and simply add the content to the page as normal above the footer.
7. The search button on mobile devices doesn't seem to work also. When tapped, it doesn't actually display the search field.

Other suggestions and improvements from yourselves are welcome too.