All filters are not created equal. The quality of an optical system is only as good as the weakest part of it. If you buy a cheap, image degrading filter, then even the best lens will look like Coke bottle glass.
Before you buy a "protective" filter, ask yourself what you are trying to protect your lens from.
If the answer is dropping it and breaking the glass, a lens hood will do a better job of protecting it. If the answer is dirt, a camel hair brush will do a better job.
No filter is required, but many photographers see a polarizer as a must have accessory.
Many photographers, myself included, see "protective" filters as a waste of time and money.
Is it recommended to always have a UV filter on your lens ( protection?)?
UV filter salesmen always recommend this, yes. Just as camera salesmen always recommend the "extended service agreement". Some people do find spending the money (and putting up with the potential reduction in image quality and focus speed in the case of UV filters) to be a fair price for the extra piece of mind. Otherwise are fine just taking their chances. As Wheatfield says, filters don't really protect against much, and much of what they do protect against is protected far better by a hood (and/or by an insurance policy). But some people just can't sleep at night without whatever small amount of extra protection the filters provide, and are willing to pay the price for it, and that's fine too. If you browse these forums, you'll dozens of similar threads with pretty much the same debate. Some find the tradeoff acceptable, others don't.
Is a polarisez filter a must or an artistic add-on?
More the latter although "artistic" implies something more esoteric than it really is. It's something that would be counterproductive 99% of the time, but the 1% of the time it helps, it helps a lot. So it's not something you leave on all the time - it's something you put on when you want the specific help it provides. Google should tell you all you need to know about they are for.
There's been a few threads on this subject.'To UV or not to UV'To me,the UV is my'condom'for my lenses.I would rather have it on just in case.Better to be safe than sorry!Anyway as for the polariser,get a good quality one.Have a look a the Hoya brand.
most of the lenses i bought used came with a UV filter of some type affixed. My position is that when taking a photo for which i want the best possible IQ, i remove the filter. That said, i don't own any fancy lenses with a "*" or a "limited" on it.
BUT, with three kids around the house and shooting close ups with wide lenses, i have learned more than once that a sticky little hand can reach out and smear my glass faster than i can dodge, so the UV is worthy protection. Also, those of you with pets, that shiny lens must look like something tasty because i have just barely escaped a charging tongue once or twice as well...