Mobo: Yes as long as it comes with an updated BIOS for Ryzen 2000, ASRock has been good about this. If it doesn't then you will have to contact AMD and request a BIOS update kit
https://support.amd.com/en-us/kb-articles/Pages/2Gen-Ryzen-AM4-System-Bootup.aspx that will come with a cheap CPU in order to update the BIOS or borrow a 1st gen Ryzen. Saying this many motherboards will be shipped and sold already with the new BIOS but there's no guarantee especially if you get a mobo thats old stock.
RAM: 4GB is no enough, you will want at least 8GB and in dual channel, meaning 2 sticks of 4GB. Also buy the fastest speed RAM you can fit in your budget.
SSD: 120GB is quite small, 20gigs will be taken by the OS so in reality youll probably only have 80-90 gigs left after wards for programs, 240 or 500GB would be a better choice. You can find some used SSDs on ebay and such.
PSU: For a budget PSU, I would suggest the Corsair CX450 (grey and black lettering not green) or CX450M.