The temple is really a large complex with several constructions worth seeing, but it does require some walking and, at some points, stairs. A lot depends, though, on whether you can do the visit at your own pace, stopping often, and the degree of the mobility difficulty. I saw many elderly worshipers when I visited, walking with younger relatives.

Entrance prices for foreigners - 1500 LKR ( 9 USD - depending on the USD rate), ticket kiosks will be available on the lake side of the temple. ( please refer to security they will guide you )

around 2 hours

Luogo interessante anche se molto affollato c’è una grande calca di gente abbiamo avuto la fortuna di assistere ad una cerimonia molto ordinato il flusso di persone

You have to remove shoes before you enter the temple. The quick walk from the shoe storage place to the temple is 2,minutes on cobble stones, so a good suggestion is to take a pair of socks if it is extremely hot, so not to to burn the soles of your feet. Inside the Temple it is a combo of cobblestones and smooth tiles and it is lovely and cool to walk on.

Sadly I am not the best qualified to ask. Ishani Sen's advice to avoid Poya days sounds very sound to me, and also to try and avoid weekends and major religious festivals. This I would myself try to do, if and when I have the opportunity to go to Kandy on some future occasion. Despite my own less than perfect first and only visit, I was awestruck and very impressed, and would welcome the chance to contemplate the temple more peacefully.

Yes

No, you don't get to see it. You see the place where it is.