No, it won’t improve performance, because SD cards and the like are optimized for linear read/write performance. That’s what you need when taking photos or recording videos, after all. Also, they wear out much faster than full-fledged SSDs. Reading data is no problem, of course, but Windows doesn’t just read but also write. A lot.
Depending on how your card reader is connected internally, you might indeed be able to boot from it. You can try this with an inexpensive small card, just put some Linux distribution on it.
It won’t work with Windows anyway because it refuses to be installed to removable disks of any kind.
If you keep your laptop running for extended periods of time, more RAM may improve performance tremendously, with increased cache size and all.