No, in general we do not perform this unless the solution is known and easy to implement then we might do it at our own discretion. Our extensions are written to avoid incompatibilities with 3rd party code, so it is very rare that our extension does not behave as expected with a custom theme / 3rd party code. In the event that your theme / 3rd party code causes an issue, then we will offer general advice on what we think might be the issue and we can be hired to resolve the issue if your technical team cannot handle it.
Yes, if you select he backup action. This backup will be stored on your server and we will need SSH access to perform the backup. We do not overwrite core files or alter core database tables, so in general there is not much reason for a full backup, but we always recommend that you perform a backup prior to us installing in case there is any issue.
Yes, you should make your own backup before sending us your server credentials. Extendware takes no responsibility for your store or data.
Sometimes we will do this if it works with our work schedule. You can contact suport to see if we can accommodate you.
Most extensions will work with any server operating system, but we only install on unix-based servers.