The problem with fish food is that it will go off and make a nasty mess on the bottom of the tank. It is not really much good for fishless cycling.
The advantage with fishless is that you grow enough bacteria to support a tank full of fish before you add any. It's just particularly sensitive species that need to wait - neon tetras are known to do badly in tanks under 6 months old, for example. It's fish-in cycling where you have to go slowly. With that, you get a few fish, wait for the bacteria to grow (doing water changes to keep the fish safe), get a few more fish, wait for the bacteria to multiply, get a few more fish etc.
Salts designed for fish tanks will be fine. In the UK lots of places have very hard water so these salts are not as common as in Norway, but people who want to use RO (reverse osmosis) water to remove the hardness so they can keep soft water fish have to add remineralisation salts - and in those areas with very soft water. It sounds as though your shops are well stocked with this type of product.
But a word of caution - if Norwegian shops are anything like British shops, and US shops from what I read, they give a lot of false information. British shops do not believe in fishless cycling, preferring to sell bottled bacteria. And they will tell you any fish will be perfect in your tank in order to make a sale. Always research a fish species before buying just in case the shop worker gives inaccurate information.
And another note: you say you want a chain loach, does that mean just one? Because these fish are shoaling fish and you need at least four, preferably more. The problem with them, in this country at at least, is that they are very expensive.