Long term opencart, prestashop ammendments

We have a client with various opencart and prestashop sites, they both need amending and updating, starting with some fairly basic bug fixes and tweaks but also adding some fairly complex items such a personalized messages on products etc.

It needs to be done to a high standard and within a reasonable timeframe, we are looking to build a long term relationship with a developer at a good rate.

As an example of a immediate bug fixed needed.. one opencart site has started saying "Invalid backend response.Data is not JSON." when trying to upload an image... but thats only a small problem on a long list.

If you are interested then let me know when you think you could start and what the costs for the above are likely to be. ALso ill need to be able to contact you via skype.