Regarding the assembly and cracking stuff, I've actually taught myself that (not RISC-V, but x86, arm, and a little mips and PPC). The way I did it, was largely practice by doing. Specifically, I tried to almost every weekend put some time into competing in CTFs. Focus on the reversing challenges, look for writeups on similar challenges, fail, and once the CTF has ended, read the writeups and try solving again. Rinse and repeat, each weekend you'll slowly get better and better.

Additionally, start messing around with an assembly debugger. For me, being able to step through instruction by instruction and watch as the values of the registers change, made everything sort of click. Start with making your own program in c, then debug the assembly, and pay attention to how your c code got converted to assembly.

There's also some decent books out there, I like NoStarch (there's a malware book and also hacking: the art of exploitation, the malware book is more reverse engineering, but both should be decent starting points for assembly).

Btw, picoctf is a good starter one that is hosted year round.