Everything seems fairly reasonable. There are certainly places you could cut costs if you wanted too though. Lots of people use the UC100 USB to parallel adapter (only $100) in place of the ethernet SS.
The G540 is a rock solid platform. I've used one for over 8 years. I had 1 driver fail and Gecko replaced the whole unit free of charge well after the warranty was over. That said there are cheaper options as well if you don't need/want the 4th axis.
I think you should probably come to terms with the fact that you'll be soldering at some point in this build, haha. It's not difficult but takes a bit of time to do. but on the plus side, you can make harnesses exactly the way you want them.
Ballscrew kits are always overpriced I think, but then again I have the means to manufacture my own. If you're going thru the trouble of modeling it all up, why not just design your own and have the ballscrews machined to your specs? I know there are a few vendors on ebay that will do the end machining for you for very reasonable prices.
And on the topic of modeling. HMSexpress is cool and all, but if you want to do 3d contouring at some point you might as well switch to fusion360 now. At least for the CAM side of it. Fusion includes the professional version of HSMworks in it for free.
As for if it's worth it. Only you can answer that.