Hallo mate. I shall try to answer your questions.

1. YES, you can go straight from /71 to /100

2.NO, it will not have any impeding effect to run the old maps. The maps DVD is irrelevant to the version of your O/S

3. If you download the night mode from this forum (instead of the v.32 in this thread) the night mode is already there

As for the detailed post, just see the first page of this thread and the ' Night Mode now Available, Here.' thread. They have everything you need.