First, my interpretation of the language in your post is "buy the camera, get the other goodies thrown in for free". If that is the case, $300 is over priced.
Now, for the whole kit, let's look closer.
About a year ago, when I was lusting after one of these toys, it seemed you couldn't touch one for under $200. The camera as you describe would fetch probably $225-250, maybe more depending on condition.
After seeing Jim Galli let a crown go for a really low price, I decided to recheck eBay. It does seem that prices have dropped on these toys.
Really nice ones still seem to fetch a good price. This one went for $271
http://cgi.ebay.com/CROWN-GRAPHIC-4...538660376QQcategoryZ15247QQrdZ1QQcmdZViewItem
The Optar is possibly a better lens, but comparable.
This one sold for $91, in not good shape.
http://cgi.ebay.com/GRAFLEX-CROWN-G...539201268QQcategoryZ15247QQrdZ1QQcmdZViewItem
So that gives you a pretty wide range. Figure $150 for good measure.
The other toys:
4x5 holders: $5-10 each. Figure about $75.
(although I have purchased wood holders at camera shows for $2)
6x9 back:
I see them on eBay selling for $40-$70. Figure $50 to make the math easier.
4x5 tank--hard to say without more info. If it is a tank with film-holders (like a yankee or the like), it doesn't add a lot to the deal. If it is a Jobo, it adds a lot. figure maybe $25.
So, you have camera ($150), holders ($75), 6x9 back ($50), tank ($25), and you get $300. Big error bars, but I think in really good condition the camera would be worth more than the estimate.
As to the other questions:
The Crown is a pretty classic entry level 4x5 camera. Can't go too far wrong. If you need a lot of movements, it may not be ideal. However, if you are mostly after big film, it is a good find.
Here is the story I heard about the 127mm lens:
This was made as a standard lens for 3x4 cameras. Thus, it barely covers 4x5. It was made popular as a press lens. 127 is moderately wide for 4x5, so it covers more area without distortion of a really wide. Use the finder for the 4x5 standard lens (~150mm), and you are pretty sure to get your subject on the film somewhere. The press photographers supposedly would set the lens at hyperfocal distance, where it covers 4x5. Put a flash-bulb for light--lots of light so you can stop down a lot and get a lot of depth of field. Net result, a point and shoot 4x5 for moderate distances (the sorts that a press photographer would be interested in).
Matt