Hey, welcome to the forum!
I'm sure some of the European folks will jump in and tell you where best to locate winemaking supplies so I'll leave that for them and just comment on the things I'm qualified to
1) There are techniques for propagating yeast and I think some folks here may have done it, but it's really not recommended, as yeast will mutate all on their own so what you get a few generations down the road isn't going to have the same properties as what you started with. What I'd suggest until you can get a supply of yeast is doing something along the lines of a sourdough starter - Make a starter with it (I'd suggest a 1 litre jar) and keep it well-fed with something like apple juice and in the refrigerator until you need to use some, let what you take out come to room temperature slowly before you pitch it, you might want to use it to start a starter for each batch just to boost your yeast count. Other folks may have better ideas but that's what I'd do if I only had one packet of yeast to keep me going.
2) A litre is APPROXIMATELY a quarter of a gallon, so you'll get similar results if you divide a 1 gallon recipe by 4 or a 5 gallon recipe by 20. Recipes do scale up and down, just multiply or divide everything as appropriate... I find this to be a very helpful website when converting units from "American" to everywhere else
Although this does make me want to ask you a question: why do you want to make 1 litre a week? Is that the biggest container you can get? Wines and meads are better with a little age, and larger batches tend to age better (also they tend to last long enough to age). A gallon a month might be a better approach. If you check around and read some of the many brewlogs, you'll see that very few of us drink our meads within the first 6 months, which means you'll have 24 1-litre bottles kicking around before they're worth drinking, unless you make something like the Joe's Ancient Orange mead at the beginning of this thread, or maybe a Sima recipe like this one (scaled down) might be a neat place to start.
3) It doesn't have to boil dry, just a good boil for about 5 minutes or microwave it until about half the water's evaporated. If you can't get your hands on anything like energizer or nutrients, check out this thread, I think it's got suggestions on amounts. I usually use 2 tsp per gallon in half a cup of water, boil until it's about a quarter-cup, but I also use proper yeast nutrients and energizer as well. There are more threads on substitutions you can make when you don't have access to or don't want to use the usual additives, I'd suggest checking out the forum search tool, start with search terms along the lines of "natural nutrients" or something like that. The two recipes I suggested above use bread yeast, they don't use any of the storebought stuff and are fairly predictable even without the use of a hydrometer.
4) Ordinarily, no you don't, usually for dry yeast you just want to rehydrate it, but if you're trying to use one packet of yeast for the rest of your brewing career you probably will want to... mix up your must in one container, add your rehydrated yeast to another, and just keep doubling the volume until all the must has been added...
5) Honey itself doesn't have a lot of the nutrients that yeast need to multiply into a strong colony, which is why we often recommend adding raisins or something if you don't have yeast nutrients available. You won't taste the raisins in the finished product anyway, even if you add a considerable amount of them (up to a pound per gallon of raisins will quite easily hide behind any other flavour)... Do a search on "show mead" (a mead with honey, water and yeast as the only ingredients) and you'll see that they often take a looooooong time to finish. Mine did. Presuming it's even finished now.
If you want to make decent mead, I suggest you start by reading the Newbee Guide off to the left there, if you haven't already.
Good luck with it!
"The main ingredient needed is 'time' followed closely by 'patience'." - The Bishop 2013
"When you consider that laziness and procrastination are the fundamentals of great mead, it is a miracle that the mazer cup happens." Medsen Fey, 2014
"Sure it can be done. I've never heard of it, but I do things I've never heard if all the time. That is the beauty of being a brewer!" - Loveofrose, 2014
"I tend to....um, er, experiment, and go outside the box. Sometimes outside the whole department store." - Ebonhawk, 2014