I've spent the past 3 months or so working with F# with zero .net experience - I love the language alot but yeah, you will eventually end up learning C# (not that that's a bad thing) if you want to use its extensive and powerful ecosystem.

If you look at the MS documentation for .net, none of the examples are in F#. I guess that's okay since it probably wouldn't be idiomatic F#... but still, the docs have examples in C#, VBA, and one other language (I think it might be C) but no examples in F#.