At the end of the day, it's down to the 2 of you, and what you feel comfortable with.
I'm with your FH in that I can't abide hymns at weddings and funerals - but that's because I'm not religious and so singing them makes me feel very hypocritical. I've also found that at religious weddings that I've been to, half the group don't join in, because they feel uncomfortable, or don't know how the song goes, so it's often been carried by a few people who can't be heard over the organ.
That said, if you have a good number of people who will participate, you should be fine. I think that 2 hymns and a psalm is good number - especially if your FH isn't keen, after all it is his day too.
Regarding the length of the service, I personally think anything much over an hour is too much, but anything up to that is fine.
Our ceremony is going to be just under an hour, and will run more or less like this:
- Music in for BM's & myself (my brother is playing his guitar for us )
- Registrar/legal part (the bare minimum), Sign the register so the registrar can go
- Humanist ceremony with celebrant:
- Reading 1, Vows, Ring exchange, Reading 2, Handfasting, Jump the broom and out for confetti and fizz
All in, it should be between 40-60 minutes. I guess we'll have some music playing when we're signing the register, but I'll probably just get my brother to play some more.
Hope this helps!