Right now there is no useful RISC-V hardware, there is nothing to talk about. And suggesting it to newbies moving from AVR is plain cruel.
Why cruel? He's a hobbyist. He doesn't have a boss who yells at him every morning pressing for results (whatever this is in his mind). Why do you think that repeating LED blinking/LCD driving exercises with STM (after he already did exactly that with Arduino) will fill him with joy? Looking at the first ever open-source RISC-V processor, which does not yet have a fully operational ecosystem, may be something differed and much more rewarding. I think Bruce is absolutely right suggesting this. OP is free to choose what he likes.
OK, I somehow got interested in the FE310 board. It starts out with a 48 pin chip so, by definition, IO is limited when compared to a 100 pin chip. But it does have a UART, 3 PWMs and SPI (master only) with 3 slave selects. Getting to the details is going to take a bit more reading. It's also fast!
It uses an external Quad SPI flash for program storage (there is a 16 kB internal instruction cache) and it has 16 kB of data SRAM. AFAICT, there is no analog input or DAC output (other than PWM). There doesn't seem to be support for Ethernet (like in the LPC1768, among others). No USB Host or Device AFAICT.
So, pretty spartan by some measures. But, as pointed out, this is just one implementation. Something to get started with. But, at $59, it's kind of expensive when I can buy an Arduino Nano for about $5. And the Arduino Nano is pretty well understood. I'm not comparing speed here, the Nano is SLOW! The RISC-V is FAST!
Intertia, that's the problem. Static inertia says "Nobody is using this, prototype projects aren't available, why bother?" and dynamic inertia says "I'm using ARM, it's a RISC core, why bother?".
The ISA is irrelevant to the user in most cases. They want to pump C in one end and having blinking and flashing come out the other end. At the hobby level, I'd be willing to bet that most users don't know, nor do they care, how the NVIC works.
Think of how different the PIC, AVR and ARM ISAs are. They are wildly different and, yet, the PIC 16F series is still being sold. By the bazillions!