On buying components:
We Americans are very fortunate in that we have very little duty on imported goods. I understand this is not true of most foreign countries. Once you get through with exchange rates and wire transfers and the like, the cost of a component could easily double, triple or worse. The Internet is a good resource. But shop around. Small mechanical children's toys sometimes have just what you need for a lot less money. Specifically when it comes to motor and motor gearboxes. Old computer parts are also a good source of lightweight connectors, wiring and switches.
Helium:
As you are probably aware, most of the helium in the world is "mined" in the United States. As everyone familiar with airships knows, Hydrogen, it's lightweight counterpart, was responsible for the loss of the Hindenberg and most of the WW1 dirigibles - and in an awkward way responsible for the incendiary bullet! However, you should always be able to obtain Helium from a welding supply shop because it is used to shield the arc when welding aluminum (hence the term "Heli-arc"). The United States strategic reserves of Helium have recently been put on the open market, so the cost should be decreasing. While we may have various chain stores that carry it, you may not. Try a welding shop.
Motors:
It is generally better to find the lightest, smallest, motor and gear it to a lower RPM than it is to use a heavier motor. Even a tiny motor turning 15,000 RPM can be geared to produce good propeller speeds and thrust. It takes very little effort to propel a dirigible. So you get an idea of the force required, take a party balloon filled with helium and ballast it to neutral. Push on it and see how much force is required to move it. It isn't much! I once had a dirigible that had a large 18 cm propeller and turning only 50 RPM it would propel the dirigible (12 foot long). Slower props are better, and high speed motors are better. The Swiss build some very nice small motors, and of course the Japanese. Sometimes you can find an adequate motor in the most unlikely place - like an electric water pistol! Plan on a motor and propeller weight of less than 15 grams. Note: this also affects your flight endurance.
Language
Well, I hate to admit it but the language of aircraft is English. My failing in the plans, particularly the flight test portion, has a lot of idiom usage. If you have a problem, just email me and I will try to explain. My French, Chinese, and Arabic are pretty bad but my broken English is very good! I also speak some German, I can get Spanish translated quite easily, I also speak Thai (from a previous life). I had an English neighbor for a while and found that we were often separated by our "common" language. My hope is that the plans are complete enough to be self explanatory. Pictures are worth a thousand words right?
Metric vs Inches
The plans are in Inches. If I get enough foreign interest, I will carry plans in both units. Until then, you are burdened with this awful /32, /16, etc. of the arbitrary inch. What do metric people call an inch worm? Can you walk a Kilometer in someone else's shoe? Well anyway, I use grams for weight so I'm halfway there.
Supplies
Balsa should be available at your current source for airplanes, but the Mylar is one thing that might prove tricky. I think it's possible you could buy "space blankets" which have a gold or silver deposition on the mylar. Buy one and check the thickness. It should be .001 inch or less. Piecing these pieces together might make it weigh a little more, but it might also be the difference between looking at the skeleton hanging there (or worse a finished project) that is not flying. I don't want to stock parts but I could probably help foreign customers with some of the special lightweight items if they are really in a bind. Note: most of the lightweight components are long lead times - even for me! What I recommend in the kit I know works. If you want to make substitutions, you are on your own. If you are not flying, the first question I ask will be how much this or that weighs. That's the difference between flying and hanging.
On props...
I cut my own props from 1/4 inch (5mm) balsa sheet. They weigh about two grams each. Build some extras because if you whack one on something it will break and be thrown out of balance. If it is out of balance enough it will break the motor mount loose. This is not good. I highly recommend you run the props on the output shaft of the motor and add scotch tape here and there until it is running smooth. My technique is a little different in that I had available some quite sophisticated dynamic balance equipment (also my business). DO NOT use wooden or plastic props for gasoline RC engines. These are obscenely heavy for RC LTA. You can use feathers in a cork if you wish (it works really well actually), and because of the lightness, balance is not so critical. They are not good in reverse though. I won't go into details on what pitch to use, diameter, etc., as this is all covered in a multitude of texts elsewhere.
Liability
This is something we Americans have come to accept in our everyday lives. As long as you build according to the plans, use helium, and fly indoors, your liability exposure is near nil. I expressly and highly discourage outdoor flight since the power company will really get angry if you get several square meters of Mylar in their power lines! It might also prove irresistible to a kamikaze pilot. When I fly real airplanes, I (and many of my flying freinds) routinely alter course to "kill" the stray party balloon, but a three meter dirigible might prove lethal I'm afraid. It probably also shows up on radar really well. I have enough problems just promoting RC LTA without having someone try to sue me for something as idiotic as this... you are forewarned! The worst thing that will happen indoors is the dirigible will get stuck on the air conditioning inlet duct and they will have to shut down the air con to get it unstuck. It has happened.