I have had a client who is 10 years my junior and has been incredibly loyal to me for several years while taking a break from the our industry, to focus on my career.

We have a good relationship and have an appointment scheduled for this weekend. He has expressed an extreme interest in having me humiliate and dominate him.

This is not a service I have ever provided.
I am definitely a sensual nurturer.
I am very authentic, sensitive and down to earth and humiliation does not come naturally to me... AT ALL! In fact it makes me feel extremely uncomfortable because I don't like being humiliated myself.

He would like to give me his money in small bills and wants me to make him count it out, over and over again to make sure it's all there, spank him when I catch him looking at my 36G's and tell him when his next appointment with me will be and when. He wants something weekly.
A standing weekly? Sounds GREAT, I know, but I know absolutely nothing about domination.
Two hours of beating this guys ass and making him count one dollar bills seems incredibly over whelming to me.

I want to give my loyal client, whom I absolutely adore, what he is asking/paying for. But at the risk of sounding like complete Wuss, I am afraid of failure and disappointment, even though he's totally submissive.

All input is appreciated, but any Dom's out there who can give me some insight? PLEASE?!

Domination is not something IMHO that someone can tell you how to do, or you can read a book and perform.  You can Google away, but actually performing it is completely different.  It requires shutting off that "nice" part of you.  It's not easy and not for everyone.  If I were you, I would tell your client the truth, so you don't lose him by not meeting his needs and fulfilling his fantasy.  Not only does being a dominatrix require work and practice, it can be mentally tolling.  Good luck and you're welcome to PM me if you want more info.