use 1/2" fittings and 7/16" tubing. Thats what I use right now and the tubing is tight around the fittings to ensure that it stays on. That doesn't mean you don't need to use hose clamps though. Zip ties work well in this situation. Try and get metal fittings if possible. Its easier to slide the tubing on and off. Plastic is horrible. Petras Tech should be able to take international orders. Give them a call and ask them.
The Swiftech MCRES-Micro is great. I currently use it and it works very well.
And about the fluid, yes you mix all three into one. For the Pentosin, its an antifreeze so it does contain ethylene glycol so keep pets away from it. Mix it in a 9:1 ratio with water. So 9 parts water, 1 part Pentosin. For the PT Nuke, there are instructions on there. 2-3 drops should be fine.