It is a very good idea to have an online equipment rental marketplace as you can connect many different companies and also your customers will be able to search for the equipment they need from multiple sources.
You can start this business by renting out small tools or anything that you do not use on a regular basis.
There are many online rental per build scripts that you can use or you can create it from sratch. For more details refer to my blog https://techwink.net/blog/create-a-multi-vendor-marketplace-using-wordpress/

As far as marketing goes, I would suggest creating high-quality content on your website which talks about the benefits of renting out tools and other things like how much time it takes to learn how to use them etc. You should also create some sort of landing page where people can sign up for updates about new products that are coming soon. This will help generate more traffic to your site and at the same time generate leads for future sales opportunities.

I've successfully helped over 150 entrepreneurs, startups, and businesses, and I would be happy to help you. Please send me more information before scheduling a call - so I can give you maximum value for your money. Take a look at the great reviews I’ve received: https://clarity.fm/ripul.chhabra