Finances are an aspect, that you really shouldn't underestimate. Most of the gardening stuff doesn't cost much as a single position, but in total you won't come very far with 1000€.
You need earth. To get the right earth it is important to cooperate with someone who has a clue about agriculture, as compost earth and the earth for flowers you get in the flower shop will with a high propability kill your small vegetables... the knowledge about earth, plants... I will share in the next how to parts. Let's stay at money stuff. You need plants, wood, perhaps grass in rolls... it depends on your project, so make an exact list, not forgetting about tools... if you have a list you can start looking for money. There are state sponsors, in Austria it is BMUKK or Vienna specific MA7 (Magistrat for cultural issues). What they want from you is an excel sheet, you have to make a prognosis about what you want to do, how much time you will spend on it, how much money is your time worth... do you need flyers, print costs, do you need money for drinks and food for the people working with you... don't hesitate to write every little position down, that could cost you money and send it to all cultural institutions, that could help. Normally these institutions won't give you the whole amount of money, you you apply for. These institutions need minimum one month for considering your case, so it's good to apply min. two months before you'd like to start as they don't have regular dates for discussing the budget, and that you see some time before starting, if you'll actually get some money or not. Another thing is, if you do the project in the context of a design festival, check what institutions are sponsoring this festival, as it is possible that if they are sponsored by an institution, where you also want to apply for, you won't get any money from them, as the whole festival is sponsored yet.
After that check out possible private sector sponsoring. There are two parties, one from which you'd like to have money, here you can first apply at any possible partners that have to do with ecology, bio food, green lifestyle (and if that doesn't work go to banks)... and other partners can be companies that will sponsor stuff like seeds, plants, earth, tools... find out what are the companies in your countries, call them, go to them, present your project, cooperate with ecological companies, they have mostly an ideological background and are more open to help you, your plants will be bio, that's healthier and it gives you at the end better PR. I can not tell you how much money you'll need at the end, but for a project in the scale of ours it's no failure to have 4000€ plus. With money everything is just easier.
That's my statement about money, so we have the basics to actually start in the next how to's we'll discuss a bit more about the actual plants, earth and so on.
… to be continued