I agree that it is totally up to what you and your child decide, what your child can cope with and their tiredness levels, amount of homework given and so on..
My DD does a lot and I often get the rolled eyes from other mums who think my DD does too much...
My DD does:
Monday 3 hours Gym
Tuesday 2 hours dancing
Wed 3 hours gym
Thursday - day off
Friday 3 hours gym
Sat - day off
Sun - 3 hours gym.
She is 8 and also in year 3.
But her levels of activity are phenomenal, she has zero ability to sit down and just is a very active and always has been (which is why I sent her to gym, to calm her down, in the first place).
The other week, I took her to a 3 hour gym training session, and in the afternoon we went out and she saw a gym friend there...and did four hours of running around and doing gymnastics on a big field.
Last week she came out of another three hour training session and did 107 backward walkovers on the way back to the car.
Last weekend, she stayed at a friends house overnight, stayed up to 9.30pm, woke friend up at 6am to start playing, went for a 3 hour training session at 9am (on the way home, friend was knackered and commented on my DD 'MrsLetchchild is never tired') but my DD came home and had a two hour bounce on the trampoline.
Sure, I get people insinuating all the time that my DD does too much, how does an 8 year old cope and so on... but I know my daughter best and I know she can and does cope. More than that, she thrives. She's doing well at school, I never wake her up in the mornings and she has just asked me if she can start swimming lessons on her day off. I said no 
.
Honestly, everyone has an opinion and every child is different - what would knacker out another child would be nothing for my DD, so you have to do what's best for your child, not what someone else thinks.
PS Your child's hobbies sounds lovely to me :)