HI Olive,
I have been practicing shiro for 8 years. As a beginner, the safest thing to use is a blend of sesame and sunflower oil (50/50) as it is the most tridoshic and easy blend to make.
Giving a treatment with a hand held is possible, no worries there, but I much prefer to use a stand. I have had hundreds of shiros, and everyone does it differently. I recently had one with a pump, where the therapist held the end of the tube over my head for 20 minutes. She was absolutely amazing! I really did not feel her wobble at all. My best suggestion for holding the pot in the beginning is to rest your elbows on either side of the clients head, then be seated at the head of the table.
You may eventually love giving this treatment so much that you will want to invest in a set up that holds more oil, but for now, what you have will work fine. I actually have the set up on that site, the hand held pot you have and one other one. My most preferred method is without a pump, because that is the way I was originally trained. However, having recieved both methods, I can tell you there is almost no difference.
Enjoy your new treatment! It is my very favorite thing to do!
Namaste'