Will that be the entire scope of the business?
Do you have a local shop you can work with, maybe even have an office in? This will be helpful when ordering, holding, etc. If you can have an office with a sign on it there you will get new business from it too.
I run a pet care company that in addition to aquarium maintenance does dog walking, pet sitting, dog waste removal, etc.
The aquarium maintenance requires a little more infrastructure. You need an RO
system, water holding containers, at least a few tanks to keep livestock in, and an area for dry goods. As stated, experiences with all types of aquariums is essential, or at least know your limits. That is a very important thing to know and accept, your limits. If you can't handle a 500 gallon reef tank in a restaurant, don't try. At most subcontract it out to another service company and let them be responsible (or just sell them the lead).
One thing that you may not expect is that you don't want to make the tanks TOO easy to maintain. I have developed a way of setting up tanks that requires VERY little effort for me to maintain them at home, but when applied to a client's home you may find yourself defending your fee when you are in and out too quickly, or they may watch you do it a few times and think, 'I can do that and save myself some money.'
If you will be ordering your own dry goods you should check out Royal Pet Supplies. They are based in New York and have been easy to work with, willing to UPS orders of at least $50 to your door (not every item available for UPS, more reason to find a LFS
to work with).
A website is essential in today's world. I did my own at first and enjoyed it so much I started a second business, just web design. If interested in more information please PM me. The good thing is that some photos really make a huge difference. Take pics of any tanks you take over to show a before and after. Take a video of a couple really nice tanks, they also look good on a website.
Don't undersell yourself. You are worth a certain amount. Selling yourself cheap does not help you, it will cost you money. If someone doesn't want you because of price alone think twice before dropping your price, make sure it is worth it. Clients who are focused only on price are not going to be your money makers, but you also need to know where to draw the line.
Double check mileage. Your fee should be able to compensate you for the mileage you put on your vehicle going to and from jobs, your time, AND still leave enough left over to take home. Base it on the IRS, currently $0.51/mile or actual cost, whichever is higher).
I have more but don't have time right now. Please post any specific questions you have, I will reply again later this evening.