Server peek by Own-IP-Calls?

Absolute URLs are not the reason for your problems. Relative and absolute links stress servers the same way. There can be a problem if you load all your content at once (e.g. hundred of images). You can solve this issue with AJAX (loading content on demand).

problem with wp theme uploading to server..?

Codex has some step by step instructions on manual theme upload. In case of issues it is also worth checking if theme structure and meta information are adequate and in line with technical requirements. There is also Theme Check plugin for automated testing, but it’s unlikely to help if WP can’t properly detect theme.