Should be fine. for the 5450. Youll need the cx500 for the 7770 upgrade though!
It probably will work. although Amd recommends 500w supply, better to stay within the guidelines. http://www.amd.com/us/products/des
Do you know that they recommend 500 watts or greater for the 7970 as well ?http://www.amd.com/us/products/desktop/graphics/7000/7970/Pages/radeon-7970.aspx#/2
Do you know that the 7970 can draw 3x as much power under Furmark load ?http://ht4u.net/reviews/2012/amd_radeon_hd_7700_test/index17.php
How about the apu? It's a pretty low power item http://www.xbitlabs.com/articles/cpu/display/amd-fusion-intel-core-i3_8.html#sect0
Hmm, 100 watts for the 7770 running Furmark + 70 watts for the basic system running LinX
With the specs he gave us, there's not much chance of the OP ever putting a 50% load on a CX430, it's more than enough