As said, buy new clips from citroen or ebay for a few pennies each. They absorb all the shock when you get a bump.
If the brackets are fucked then by all means glue it, but i'd prefer to use plenty of masking tape instead of duct tape as it can be a bit harsh and sticky so may ruin your paint or leave it's residue behind and dull the paintwork.
For the side skirt i'd rest it on some books, tins, cans, scissor jacks etc just to support it...unless you need to drive it but i wouldn't recommend driving it whilst the glue sets sicne it's probably a bit wet outside, might effect how well it bonds if the water gets in somewhere.