There are not any market traders professional federations in Spain similar to the UK.
A lease on a shop should be a straight forward process. BUT!
1. Are you getting a straight rental contract? or is it a proper Lease?
2. Take care that you have a right to continue renting after the intitial term.
3. You should be looking at a 5 + 5 year rolling agreement.
4.If your business is a success, will the lease allow you to sell your business.
5. To cover yourself get a clause written in that allows you to give a months notice at the end of the first 12 months, but allows you to continue to the full term if you wish.
The number 1 rule is sign nothing until you have had the contract looked at by a lawyer.
The number 2 rule, never trust a landlord or agent.
The number 3 rule use a lawyer who speak good English.
Recently had a long conversation with some English people who signed a “lease” on a shop, paid 3 months rent as an ingoing plus 2 months rent up front. After 5 months the landlord wrote to them to remind them the lease was ending - They had signed a 6 month contract! For which they paid 9 months rent with no right to stay once the shop was up and running!
You will need your NIE number sorted before you can sign a lease. Go find a local English speaking Gestoria, they will sort this for you and get you set up as a sole trader, advise you of the best system for your particular business to pay your taxes and deal with the tax office for you. If it is a small business you may be best to go on a ” modular” tax payment and pay a set tax every few months. Remember the monthly social security payments are quite expensive.
You will also need a licence which can vary from 700 to over 2000+ euro depending on your type of trade. You will also likely require an architects plan of the premises to submit with your licence application, these can cost up to 1,000 euro.
You may find this of interest http://www.spainbusinessguide.com/guide-to-buying-a-business-in-spain.html
(it is about opening a bar in Spain but does have some useful tips and do?s and dont?s that apply to most businesses)