This, and then you’re only limited by the drives themselves for speeds.

Is this a brand new engine? Using 90/10 concentrate coolant is fine More of the concentrate the more chemicals are in it that will help keep the system clean.

Yes water does have the advantage of being able to dissipate heat more. But you "shouldn’t " have to worry about that unless you live in a hot climate, ie 35°c+ average thoughout the week.

But if you really want to you can drain some into a tub/jar and top it up with distilled water. Then find an appropriate place to dispose the hazardous chemicals.

Generally no… But with the damage on the rim next to it, anything’s possible.

A new timing belt wouldn’t have wear marks on it. But this photo does…

That doesn’t look like a new belt…

You’re gonna need to rotate the engine till the marks line to to be sure…

How long is the cable ?

Internet issues can be from any link in the chain going to/from the source.