Your plan sounds good. Starting with part time is a great plan to see what you can afford. You are the owner so it is totally up to you how you structure the pay as long as it is within the labor laws that apply in your area. As for mileage we do not pay mileage - it would literally put me under. We do a flat 170 per month gas reimbursement.
If I may share my experience with you?
I like my employees to be independent. I used to drive them around and it was just such a hassle for me. When we hire we hire only with a vehicle. Right from the start they have to be at the job on their own. This also shows how they understand to be at the job 15 min earlier to get their supplies sorted and check notes on the job.