Welcome aboard to the CD Freaks forum
As your DVD recorder is a PAL recorder, the first issue you have is likely due to the recorder's inability to convert from NTSC to PAL. Most VCRs offer NTSC playback, however very few will actually convert the picture to PAL, but instead output a PAL-60 picture (NTSC frame rate & lines with PAL colour), which most TVs are capable of displaying. This means that while the VCR part of your DVD recorder can play NTSC tapes, it seems like the recorder will only record from a PAL-50 source.
For the 2nd issue, there can be a combination of issues. I have encountered people have problems taping from VHS to DVD from low quality tapes as the DVD recorder would falsely detect VHS interference/noise as copy protection and stop the recording. If your VHS tape has several recordings on it, it could also be that when the first recording ends, the DVD recorder assumes the noise or interruption in-betweeen is the end of the recording. Just to rule this out, I would recommend trying to copy a good quality VHS recording to DVD (of at least an hour in length) and see if it stops during this. If so, then there is likely a fault with your DVD recorder.
Finally, for the 3rd issue, it could be a bad signal cable, connection or tuner board on the DVD recorder. For a start, I would recommend trying another signal cable between the wall socket and the DVD recorder as well as making sure the RF cable is pushed in as far as it can go at each end, however if this does not help or if jiggling the cable at the back of the DVD recorder causes the picture quality to vary, then it is either a faulty RF-in connector or a faulty tuner board in the DVD recorder.