Need Help Choosing Engagement Ring..Please Help. Thanks :-)

Hello All :-)
I am so glad to have found this website. I am new to the whole engagement and wedding ring picking out thing, and need some advice. I am an early childhood teacher, and do not want a big ring that would get caught on anything. My hands are always in the water, so I would need something that would last much longer (i.e. platinum vs. white gold). I found my dream ring on the Blue Nile website and it is listed with a matching wedding band. I am posting the links here. Please let me know if this carat size would be too big or if I could decrease or increase the quality ( my guy and I are on a budget, so please let me know if I am way off). I am not really a jewelry wearer, so I really don't know much beyond my research on the four Cs. Thanks in advance for all your help. I really appreciate it. :-)

http://www.bluenile.com/design.asp?filter_id=1

http://www.bluenile.com/diamonds_details.asp?pid=LD00129828&query=2&filter_id=1

http://www.bluenile.com/product_details.asp?oid=4086&filter_id=1

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