I believe in the US we generally use a 1/2" shutoff valve in our kitchen and bathroom, is that what is typically used here?

Sorry for the lack of a better term, but I am referring the shutoff valve that connects to the hose which then connects to the faucet etc.

Secondly out of curiosity, why are all the pipes here PVC while back home its galvanized steel or copper piping?

Is it cause of the cost?

Usually the interior pipes are 1/2". Basically, PVC is used here because it's cheaper and easier to install, but copper (expensive) and stell are avaiable but not normally used.

You must be old school with copper/steel pipes most today is pec pipe

Yes they are 1/2", BUT the US uses NPT and Thailand is BSP.

These threads are sufficiently similar that they usually mate without issues so Stateside fittings will be fine.

Basically because there is no need for central hot water (if required for shower it is point of use) so normal PVC pipe works well - cheap/fast/easy and long lasting. Steel used to be used but rusts out quickly and copper is very expensive. Hot water plastics are not common as low demand. As said the thread is different and it is enough to be a factor at times - as simple Italy made shut off taps are available everywhere - and if you really need chrome they are also available - I would not even consider using US fixtures/taps.

Be aware that all plumbing fittings, at least the ones I have come across here in LOS are NOT taper thread (like in the US). This means they will not tighten up as you screw them together....the fittings will bottom out first. I have found that 17 wraps of the white teflon pipe thread tape (make sure you wind it on so it does not strip itself off as you screw it together) will make for a drip free joint. I did every cm of plumbing in my house and no leaks. If working with PVC fittings, hold them together for at least 10 seconds after you glue them to make sure they don't crawl out (due to capillary action) and leave you with a substandard fit. ett

You should not need teflon tape on connection house if you use the washers as designed. Just a snug fit will provide seal (and I run 60psi pressure). The only time I need tape is for male thread taps into female fixed pipe connections. For the normal flex hose using washer (or O ring) with two female connections there should not be any need for tape. Although have had to use tape on some toilet sprays (internally) due O ring not being up to the 60psi pressure and allowing leak).