My brain thinks Felix is going to enter the top 100 names soon and I'll be bummed it's that popular. My "second son" has been named Felix since his older brother was born though and all pregnancy I just thinkhe's Felix then i have to remind myself he's not.
You might take one look at him and think 'Felix' and it might just feel right from then on! Are you having a boy? or just having trouble with boy's names?

I think Marvin is very cute. Arvin not as cute. Ferris reminds me of ferret or ferris wheel. With Rover, I doubt you would ever escape the connotation of Rover the dog (but that might not worry you anyway).

Marvin and Espen, I kinda like it! I have some more Z names but the n sound might not work with Espen - Zarian, Zerron, Zephan.