schorsch-lukas
Apps2SD adds functionality (omitted by Sony) back to Android - but it is not a panacea. It does not change how much space is available on device /data partitions and each application moved to SD leaves behind a bit of itself anyway. If you really would like to get rid of space limit you need to repartition your device (in addition to Apps2SD) ... Just look for repartitioning discussions on the forum - default size of /data partition is 40MB. I have 400MB on my device
If I am not mistaken you need to enable superuser rights in TC option's menu... Something like "Root functions everywhere"?
In regards to guides and explanation - I did not publish anything in English on the subject so far, did not have time and firmware was in heavy development. This is the reason why project page on SourceForge says "beta". First stable version was published for Russian community (which participated in development) about a week ago. Now that code is stable when I have time I will probably update project page with English guides.
From time to time I answer questions here for people who are brave and do not want to wait...