2) Tile cracks - Not really. In fact, homogeneous tiles are sturdier than ceramic tiles. You can read a summary of the differences at BCA's link here: https://www.bca.gov.sg/Publications/EnhancementSeries/others/design2Ch3.pdf
Hollow tiles - No such issue, as my flooring is done by my own contractor instead of HDB contractors. It is much less prone to sloppy work/mistakes as the contractor is responsible for his work. You can always get the contractor to rectify the parts which you are not satisfied with, up to a reasonable standard.
Dirty grout - Yes, I foresee that the grout will turn from white to gray as time goes by. Will have to scrub the floor or to re-lay new layer of grout in the future. I think this cannot be prevented unless you use groutless flooring such as vinyl. But then again, we are against vinyl as it is not waterproof and is more prone to wear and tear.
3) Yes, easy to maintain. Just wipe with a cloth/wet wipe/paper towel. The oil/water stains goes away easily.
4) We do not have any regrets in the renovation (eg layout, position, design, carpentry). But I would do these things differently:
a) Buy my blinds earlier - We are currently awaiting for the installation of our blinds which can only be installed in Mid Aug as they require 4 weeks to customise and prepare the materials. In the interim, we are using old bedsheets to cover the windows.
b) Not buy my MBR TV - Super un-utilised. Only turned it on once to check whether it is working. Most of our time are spent in the living room.
c) Install a "washing point" at service yard - Currently I am washing the dirty cloths/vacuum at the kitchen sink. Wifey is not very happy with mixing of dirt cleaning together with food cleaning at the kitchen sink.