Questions from a newbie

Howdy, let me give you some background first. I bought a couple of
baby orandas (1.5") for my daughter and a eclipse hex-5 tank knowing
that the goldfish will growth soon and that 5g is not a good home for
them, but the idea was to start small. After 3 weeks they are now
2.5".

I wanted to wait and learn before buying a proper size tank. I
understand now the pain of cycling a new tank, specially a small one;
I've been doing 50% water changes every 5/6 days and finally I have a
clear tank and ammonia and others indicators finally under normal
range. I'm planning to keep the current tank as a hospital tank or
maybe I'll put some really small fish now that is cycled.

I'm ready to buy a new tank and I have some limitations to consider:
physical size of the tank, price and filter performance for the messy
goldfish.

I would like to stay in the 36" W, 15" L and up to 20" H range. I
found several options that I can afford:

29g - Marineland Eclipse 29 [glass] - Filter: one Eclipse 3
45g - Clear for Life Double Eclipse 45L [acrylic] - Filter: two
Eclipse 2
55g - Marineland Eclipse 55 [glass] - Filter: two Eclipse 2
(larger than I want but still a possibility)

My idea is to look for a double filter to have a backup in case of
failure and to have more filtration power for the goldfish. I'm
looking to have 2 goldies for the 29g, 3 for the 45g and 4 for the
55g; and no other fish, is this ok?

I'm really a newbie and I don't anything about filters and brands, but
I kind of like the simplicity of the Eclipse filtration and their bio-
wheel filter.

Does the Eclipse be enough for the number of goldies that I'm planning
to keep? I'm a little concern on that, no previous experience so no
point of reference.

Another question, when I change water what I'm supposed to do with the
bio-wheel fitter? Put it on existing tank water or submerged in the
water? For how long can be without water before damaging the bacteria?

Any recommendation for other tank/filter combination? If so, please
specify brand and models so I can search for a good deal.

Looking forward to your comments.
Thanks.