My Nexus and 18g VST should be in my hands shortly, Im actually quite nervous about the VST as the general reports are that your dosing technique is even more critical to getting good results from this basket, you have to grind a few notches finer than most others and be very consistent in the way you dose, Greg recommends reading Mark Princes report on them.
You should measure your Giotto basket when it comes and see if Greg can match a base that will fit both the VST and the stock basket depending how far it is off.
My Nexus base will fit my Synesso apparently but will be a bit loose but it should still be good.
I would be contacting your local water authority to get numbers on the average total hardness and pH in your area and then contact Bombora to sort you out with an appropriate filter system, if you have the ability to put a second tap on your sink then go with that as you will be filling it regularly and it will give you clean filtered drinking water, best of both worlds IMO.
I guess the next step after you pull a few hundred or so shots is to start home roasting if you havent already ;)