cant help much 10KM but know a little so here goes
1)if the company is so you can get residency you will need quite a bit of cash. it used to be £50,000 but i think i is now £25,000 investment into the company - this money can then be used to buy a property or start a business etc.... plus any set up costs eg lawyers, accountants and noaries fees. obviously these set up costs vary wildly from region to region and firm to firm.

2) you would have to be present in Natal with a passport and CPF no.

3)you may own 100% of the company HOWEVER you will need a person with Brazilian residency to be the administrator until you gain residencia. This is a BIG issue as you will have to know and trust this person implicitly as until you can become administrator they will have access to the company accounts and be able to do anything on behalf of the company. I believ some big law/accountantcy firms offer to be administrator for you until residecnia comes through but this is obviously expensive.

4) you will need an accountant to set up the company and again charges vary from firm to frim. I know someone who was charged 1250 reis (approx. £380) but this was in the southern interior - no idea of charges in Natal.

5) no idea

6)not sure but with a small business doing not much business i would imagine accounts being done on a yearly basis would be ok. but you would have to check that.

I believe there are people on this site (rob and mike) who have set up companies in natal and would be able to help alot more. good luck