My opinion is that you're not ready to drop thousands of dollars on modular yet. You should learn more about the functionality of basic bits of kit (including attenuators/attenuverters) before buying a bunch of modules and a case. There's nothing wrong with learn-as-you-go. But unlike a self contained synth, it's very possible that you put together a collection of modules that really don't cover as much functionality as you'd need. You'd be better off buying a pre-configured system if you really want to be in the Eurorack environment without knowing how to purchase the parts for a custom system. In my opinion, the smaller of a system you're trying to put together, the harder it is to get something useful out of it. At the same time, because of real world budget limits... small systems are the entry point for people new to Eurorack.
The preconfigured systems from Roland, Pittsburgh, Erica, Make Noise, etc. are great if you have the budget to start there. Semi-modulars work on the same principle... except rather than being individual modules they are all baked into a stand-alone device.
Bottom-line... up your knowledge of synthesis before spending a lot of money on Eurorack. You'll have a better experience.