Over the years we have done hourly, etc. However, depending on the type of clients you plan on catching with your net, I think you should think long and hard about what makes you stand out...what are you really worth, and is it ethical to your customers? When I first got into the service business twelve years ago, I worked FT at the LFS. I had a ton of clients, and so did half of the stores 50 employees (after the rest found out how much most of us made). This made things obviously tough for retail employee morale due to the competitive nature of many.
We learned after several years in different organizations that retail, service, and hobbyists providing part-time aquarium service are all very different entities with good reason. Weekly I come across a new client that came across our name after being sold everything+ by the local retailer. We look at the list of "goodies" the retailer made their 40%+ markup on, and feel at a disadvantage trying to keep quiet on why they probably do not need that super wet/dry filter system for their reef aquarium, knowing that we have about 40 or so larger systems without them. We could care less about the dry goods markup, for our business deals not with products but keeping our clients satisfied with our service. But the odd thing is in that list of "goodies" there were no well known books from the authors that taught most of us how to keep what we now have in our tanks.
Well if you want to get involved in service... can you do this 25-75 hours per week, or do you work full-time in another totally different industry? Are you planning on incorporating...obtaining proper federal, state, and local permits/IDs...purchasing insurance...and advertising? Contracts may keep some from trying to file suit, but we have seen a few of our not so formal competitors lose more than they expected when an educated customer ...obtained an educated lawyer... and then obtained a generous portion of the serviceperson's livelihood. We signed one of their clients about 2 years ago! Not trying to scare you off, but if you are going to do this, make sure this is something you can dedicate your time to (24hrs if needed) becoming respected and successful. Hence the reason why after a long client filled day, I check the boards to see what is brewing at 2:15AM only to rise in about 6 hours for another client filled day. If you would like help directly, feel free to contact me (as long as you are not planning on setting up in one of our client's zip codes) :O)