Can I still use it with some end-caps missing?
Yes, being careful not to catch your finger on the bare frame ends.
Does it rust? Can it be stored outside?
Aluminium does not rust. By the same token, you can store aluminium outside if you wish. But best to store indoors. It is advisable to store the platforms indoors as they will wear out quicker in wet conditions.
What is the size/weight of the tower?
The size/weight of the tower is given in the technical drawing which can be found on the product detail page of each tower.
Can I paint the tower?
Yes, if you wish.
Can I use the platform at a lower height?
Yes, the platforms can be used at lower heights by moving the platform down the rungs of the ladder frame remembering to lower the guard rail or bracing also.