You can legally have just one permanencia in a calendar year. This means that even with the additional 90 days you have a total of six months. For any stay longer than that you need to apply for a residence permit....
As becoming a resident in Spain makes that you are tax-liable for any worldwide income, first of all it depends on whether you have income earnings from other country than Spain and whether or not your non-Spanish income is taxed at the country of origin...
You can have it permanently. However, legally speaking, you can only drive it for six months in a calendar year. This means the six months need not be continuous and also means every 1st of January the term starts automatically from zero. Now, let us come...
In order that any non Spanish national becomes a Spanish national they must reside in Spain for a period of ten years minimum (there are a few exceptions like oficial refugees or nationals of Spanish South America, Andorra, Philippines, Republic of Equatorial Guiena, Portugal, Sephardies…all...