I don't have the Savic Hamster Heaven, but my friend does and I set it up for her, so I think I can answer your questions.
Yes, you can remove the ladders for both levels, if needed. A Syrian should be able to climb the ladders though.
I don't think it would be possible to attach tubes to the holes in the shelves.
The wheel is large enough for a baby Syrian and big enough for all the other species of hamster (if I remember correctly it's 8 inches).
No, you can disconnect the penthouse if you wish, especially during the taming period, although there is a door that connects to it.
Yes you can add levels from another cage, but the levels it comes with do take up a lot of space for more shelves.
Hope this helps
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