Congrats on the new set. You'll love it. You might check Pioneer parts for a protective screen. It's probably a good idea with a small child around. The link is below. As for size, RPTV's tend to get smaller over time, what looks huge to you now will tend to get smaller as you get used to it...
The 643's are great sets. It's an awesome set for the Costco price. Only issues are no DVI and it will not accept a 720p signal. Other than that, great line doubler, stretch modes, and comb filter. You'll love it.