Good to know about the metal tensioner and intervals, I'll have to make a good note of the mileage and date in the book and maybe a sticker in the engine bay somewhere.
Yes its wise too. I've seen some people tip ex the cam cover with the date and mileage. I usually use a sticker but after three years or even less you can hardly see it.
Keep spreadsheets now. But still its a bit tedious.
If you can still read the belt make then yes its probably not been on too long.
Still you never know if its been standing though.
As you've done it all for minimal cost (Saved on labor) then you should be good for another three years.