If you see an indy that has a lot of positive reviews posted here, you should get an idea ahead of time.  Having said that, I always bring condoms (strictly as a backup), but have never had to use one of my own as they've always provided them.  I've been fortunate in that all my visits with indys, have progressed smoothly from initial chit chat to fondling, kissing etc.  I've always produced the envelope afterwards.  It's not totally smooth, but not awkward either.  They always say thank you, and I've never had one count the money in front of me.  When I tip, which is rare, I let them know how fabulous they were and that I can't wait to see them again.  Even the ones I don't tip, I compliment them and sometimes tell them I want to see them again.  I don't tell a lady that I want to see her again, unless I KNOW that I'm going to be seeing her again and soon at that.  Many ladies that I've never tipped, I've seen again as well.  The key is to do your homework, and find a well reviewed provider.

The thing about being an indy is I get to decide my own rules, as do other ladies.  We are all different so do read the website fully if she has one, and do your homework via reviews!

My responses to your specific questions:
Donations... many ladies like to see the envelope before she gifts her time, some will discreetly count first, some won't touch it until you've left... some don't want to see it thinking this will protect them from LE.  Some can't stand the idea of an envelope at all.  Go with a well reviewed lady and check her wishes first.

Tipping should *always* be discretionary.  Tips are a bonus for great service and should never be expected.  Also many of us consider ourselves to be professionals... do you tip your accountant?  doctor?  lawyer?  No?  I'm sure they would appreciate it!  Do they expect it?  No.  If you do decide to tip you can either bring a separate envelope or discreetly leave the tip on your way out the door.

A professional should always have the necessary supplies on hand though it is a good idea to bring your own just in case.

Re: going overtime
Just as with tips, never to be expected.  Sometimes a lady may not notice and will feel taken advantage of later.  To avoid this, if you notice the time is up and the lady doesn't seem to notice, gently mention it.  "We're having a wonderful time and I didn't come prepared to extend my appointment..."  You may be surprised when she asks you to stay a bit longer!  Even if not, you will be remembered as a kind and honest gentleman who is more than welcome to return anytime.

Have fun!