Just to be sure this will fit my car http://www.scosche.com/products/productID/290
and using this I will lose chimes but everything else will work the way its supposed to?

With an SE (or SLE), that should work fine. As you've already mentioned, you will lose all warning chimes.

I did talk to an audio shop and the harness that keeps the chimes costs around $100 I can't decide if the chimes are worth that. :?

I feel it'* important, but everyone does have a personal preference. Because these alert the driver to more conditions than just an open door, your attention may be directed to events that otherwise might not be immediately apparent. This may be even more important if you aren't the only driver.

Yes you should want to keep the chimes. That price of a $100 does not seem right though, I received my harness for the chimes and did not pay a dime for it, most radios come free with installation hardware. Now what would be right is if you have OnStar and I had to pay $100 to get the OnStar harness to keep my OnStar system which I paid for. But the main harness should be free or under $100 and should keep everything!

I'm not buying a head unit because I already have one and the adapter is GMOS-05 that costs so much. I thought that this is only adapter that will keep chimes.

That type should keep the chimes. Your headunit is what makes the chimes and everything. But I believe that this is the same harness that I have. GMOS-05 is also an Onstar harness (thats what the OS means). It should keep everything.

check ebay and amazon.com

I think they were around $80 on there