The only countries that have extended temporary visa's over 3 months (to maximum 6 months) are:
- Ireland (lucky me!)
- Austria
- Germany
- Switzerland
- Liechtenstein
- United Kingdom
- Mexico
Everyone else has a max 3 months(90 days) temporary visa permit except Brunei which is 14 days.
You don't need anything in particular to get this visa except of course your passport. If you do overstay it will increase your difficulty of getting back by ten fold (if at all, i heard they blackmark your passport if you overstay so if you do come back in future then they will know about it).
If you leave before it expires then it is fine. Although if you repeatedly keep leaving before it expires and entering again soon after you are only just messing them around and it looks bad, they are copping onto this as well so and you might not be allowed in again.
As Petina said, you MAY be able to get another one if you come back, but i point to what i said above. Maybe twice (spaced throughout) or once a year doing temporary visa status might be fine, but repeatedly milking and looping through the system is just wrong and it WILL reflect on any foreigners trying to come into the country as they will be harsher and more strict on everyone because of it. A few rotten eggs spoil the rest so they say.
If you do have any other questions then do post them, that's what the forum is for