And, on top of what Sez said - prove that the renovations couldn't be undertaken while the tenant is at the property.
There's a lot of tiny details with every NTV which most people wouldn't even consider, and way too much to explain right now.
Regarding that sort of increase, I wouldn't do it nor recommend it as you've already told the tenant it would be increased by $50 - I think this would likely go to VCAT and even though your increase is on par at the $70 increase VCAT would order it back to the $50. Personally, I have not come accross this (perhaps Sez could shed some more light
) but I don't think it's good business - after all property investing is a business and should be treated as such.