Just my .02 on this. Yes to all.
You will be able to find lots of discounts on stuff if you look around. Currently promo code L on Travers will give a discount up to 25% on some items.
DX-6 is good vise in my opinion, I have one on my Bridgeport and am very happy with it. If had a good or decent vise I might want to get the DRO first but if I needed a vise the DX-6 would be the way I would try and go.
DRO, absolutely yes. Several here will chime in that have bought from EBAY and are happy, I looked at many options and when I was ready I just called DRO PRO'S. I would suggest you give them a call and just ask about after Christmas sales. I called them last year just before Thanksgiving and asked about black Friday sales early. Dan advised what they were going to do and offered to old one for me so I could just call on Friday to complete my purchase. I received a really great deal from them. The support is great and their warranty is now lifetime.
Power feed is also something I have but out of your list it would be the last of your 3 upgrades.