Hello there! Here is my response:
1. My first model that I uploaded and 3D modeled was a pencil I didn't make a sale on it until a couple months later but I was so happy when it actually sold. I was not expecting that at all. This gave me the motivation to keep on creating models and as time went on the quality of my models has increased.
2. I can't remember exactly at how many models I had up for sale that showed my sales to be regular. I'm just going to put a number out there and say somewhere between 10 and 30.
3. I noticed as I created more higher quality models number of sales has increased. I believe that its not the amount of models that you put up for sale but the quality of the models. Customers have no idea how many models you have for sale but if they see a high quality model they would most likely purchase that one.
4. For my models it seems I sell a good balance between the collections that I have created as well as the individual models. Some of the collections I have I also sell individual models of the models in the collection as some people aren't always looking for an entire collection. Also to create a collection you have to first have the individual models on your store page and then with the collection creator you can put them together into a collection. For each one of my models I like to have the models fully manually UV unwrapped, included baked textures for customers in game development, and good descriptions so they know what they will get when they purchase one of my models. I also include help documents, rendered images and more.
5. If I was starting from scratch today I would look around the internet for inspiration for things to model, go outside see if there are things I feel confident in re creating, or just look around the house and see what stands out. I would think to myself what types of models people could use them for whether in game development, scenes or other things.
Hope this information helped anyone who is reading this post. Feel free to ask any questions and I will be happy to answer. Happy modeling!