Long post i did about Targas a while back is here ...
http://911uk.com/viewtopic.php?t=116450
If you have water at the rear then its actually a seperate drain thats blocked and judgeing from what you have got out of the front glass drain tube then im not suprised .
Image below of the rear drain on the n/s/r , its a bitch to get at on that side though .. dont remove it as its siliconed in place .. you have to rod it or blow air up it .. downside is all it will do is push the dirt up the channel a bit .
best way is to wash it out but as access is so limited youll just end up getting water in the car... i can list out what i would remove if needed.
front glass tube drains straight into the gutter so a cable tie with a plastic tbe in the rubber one sounds correct to me .
Slow roof is again seperate to water leaks , i can give you costs of what it will be if needed but as these things are current only for now then i dont tend to post them as if someone in 2 years time reads this then it wont be an accurate cost.
Two places i recomend for Targa work .. One being Northway and the other where i work.
This is the only time i actually put myself forward for this as im afraid there are very few places that can do these .. i know as ive had to fix some that others had attempted and i dont like to have to redo someones elses work .
Must be something in the air for Targa problems atm .. ive answered this question via pm a week ago from a new guy and i have 3 booked in at work for dec / jan to do.
EDIT
This is one of those jobs thats far easier if i explain it on the phone and im happy to pm you my number if you want .. typeing will take for ever and not answer everything lol