Modular signals are much hotter than line level, but you can usually get by without a line level output module. I plug directly into my mixer, but just keep an eye on the gain.
You have posted many different ideas for racks in this forum, some of which might be fun and some definitely won't be any fun at all. I would recommend looking beyond brand name and matching panels to find different modules that will help you accomplish what you want. A Make Noise Telharmonic is going to sound vastly different from an Intellijel Dixie or a Mutable Plaits, and you will need to consider what utilities might help you achieve the sounds you are looking for. Why would you need a modular over software or other hardware synths? What is the benefit of pursuing your music this way?
I would recommend checking out VCV Rack to make sure you have a good handle on what is necessary to make a modular synth work.
Have fun and good luck!