You don't actually need to build an features yet. Create a pricing page, list out a simple set of features, put a buy button and see how many people click on it. Test with a different set of features and different price points.
Pecan is definitely not as light weight as flask. Creating a simple hello world requires multiple files and multiple classes. Flask is super light weight in that regard. Which is why I use flask for quick hacking on personal projects.
Pecan on the other hand has a lot of great features built in, such as ORM, built in templates, etc. Pecan is a popular choice over flask for large scale projects.