Does anybody have any tips to know whether or not my funnels are set up and what kind of abandonment rates can I then expect?

I know I can use funnel reports to find leaks and pages on which my users abandon the sale-lifecycle. I can bet nobody gets a 100% funnel completion but at what point can I justify no more time and effort spent in optimizing? What is the max one can get?

I'm currently at about 50% on most funnels I've set up...

Thanks!

This all depends on what kind of business plan you have for your website.

The best thing to do i sto plot the funnel abandonment rate over time and visualize your progress.
It will be pretty easy to go from say 80% to 60%, but lowering that to 40% may be a lot more work in comparison. Getting it to 30% will be even harder and may not only depend on on-page optimizations but also on your campaign keywords, inbound links and the keywords you rank for.

Eventually your graph will flatten out, let's say at 30%, which is already very very good. Probably at this, point the costs of further optimizing will not be worth the return you get on lowering it by the small percentage you can gain.

Segmentation of traffic types, campaigns, keywords etc. will get you there. Maybe creating different landing pages for specific keywords and different traffic types will help. Maybe you can see a way to split traffic and transfer one funnel into two different funnels.

There's no quick and easy answer here. Just use your noodle and experiment