I'm sorry that all of this is based on US situations, feel free to edit anything that doesn't apply. Hopefully this gives you an idea though.
I looked briefly into this since there seems to be demand for local pick-up and drop-off in my area. Here are a couple things to keep in mind.
Insurance starts is around $.50 - $1.00 per $1000 of equipment per month. After talking to State Farm, they said that this covers business use as well. What they couldn't answer is what happens to the rates as the claims come up. This is why you will see insurance costs with other rental places. Also, just because someone breaks a lens without insurance, doesn't mean that you will get reimbursed.
In additional to insurance costs, you are going to have other overhead with this type of business. Webdesign and maintenance, business insurance, business registration, accountant (especially when you start working with other states), legal advice, and advertising. This adds up pretty quick. The nice part is that this business doesn't require a lot of labor time to keep the parts moving. This means that any talent that you can contribute, you'll have the time. I'd say your best bang for the buck is if you can do your own web design and scheduling.
On Hand Cash
If you don't have a lot of liquid assets, any rental business can be dangerous. What happens if you have a rental that doesn't return on the scheduled time and a $500 order that you can't fulfill? You're going to lose money however you solve this problem.
This will at least have to be an LLC (if in the US). People with businesses will rely on you. A wedding photographer that depends on having his lens for the wedding will not be happy if he doesn't get it. Same goes for any other type of photographer. You are liable, so you need legal advice and protection. If you don't want to be liable, you're going to need a killer rental agreement. Either way, you're going to need professional (and expensive) legal advice.
This type of business is all over the board. It sounds great in concept, but a small collection is still around $30k. You need to have selection in order for people to be interested, but that doesn't mean that they are going to rent every lens in your collection. You need to set prices that are competitive, but work you toward paying off that initial buy-in. This is a constantly moving target. Expect to invest time in playing the game.
This really depends on your area. Here in MN, super telephoto isn't all that common. We have a lot of art (cityscape hipsters, musicians, etc). Wide angle and fast concert lenses are the popular items in this area. If you are in Montana, it would be different.
With any business, you are going to have a lot of unexpected variables. Your interest in photography will give you zero advantage in this type of business besides having a slight indication of the selection to start with, and even that won't get you far. Unlike photography, this type of business is not easily scalable. You are going to have an overhead and upfront debt that requires you to have an income.
If you can line everything up though, it could really pay off. Plus you'll have a large collection of your own to choose from which is usually why photographers start considering this.