1) If I am translating an excel file, and I have a glossary in excel format, how do i automatically translate everything in the target excel document which matches the glossary?
First, convert your excel glossary into a WF glossary (save as text only, tab delimited). Then, select the resulting file as your active glossary N° 1. Now, when you open up a segment that has a word already in your glossary, that word will be highlighted and you can treat it as a "placeable" and just insert it with a keyboard shortcut (CTRL ALT right/left to select it and then without releasing the CTRL ALT, down arrow to insert)
2) When I translate something in the source text in one place, how do I translate it again automatically further down in the document?
Did you create a TM? If so, it should propose translations on a green background for 100% matches.
3) How do I know how many 100% and non-matches I have at the end of a project? Is this calculated automatically along the way? How is this information represented to a client who uses Trados once I send them the complete translation?
You only analyse a file for matches/repetitions BEFORE starting a project. If the client supplies a TM, you will be able to see if there are any matches in that TM. If the client doesn't supply a TM, then WF will just analyse "repetitions" within the text itself. There is no point to analysing a file after the fact.
It might be worth your while to attend a day of training, or if that's not possible, maybe someone can give you a webinar. It's REALLY helpful to have someone show you everything, in addition to reading the manual. When I started out I did read the manual, but I couldn't understand much of it because I was new to CAT tools. Training really helped me to become proficient.