I adore Viljami! It's euphonic, masculine, and compared to its English counterpart William, a very youthful name in my eyes. I also think "Vil" would make a great nickname.
Heikki Willamo has made two books about Viljami Vaivaishiiri (Viljami the Harvest Mouse, I suppose). They are photographic story books about the life of harvest mice.
https://fi.wikipedia.org/wiki/Viljami
https://almanakka.helsinki.fi/en/name-days/name-day-search.html