As far as the live rock is concerned, ideally you would like to end up with 280 lbs. I know how expensive it can be, but 2lbs per gallon is worth the investment. However, 150 is a good start and will get you buy till you get the rest. When you purchase the rock online it will have to do some curing in your tank. When they say it is cured, they mean, when it leaves their facility. Even though it will be shipped overnight, their will still be some die off during its trip. This will cause your tank to go through the cycling period (again, if it has already). Then later on when you buy more rock you will want to buy it from a LFS
(local fish store) that way you can assure it is cured and wont do any harm to your cycled tank. If you do want to order more online, you can, but you will have to cure it in a separate container. You can run a search on the home page, "curing live rock" to get more information.
As far as the skimmer goes , I will let someone else guide you on that because their is a lot of conflicting opinions on skimmers. All I can do is tell you I run a Seaclone on my 100 gallon and I'm very happy with the results, however a lot of people think that these skimmers are cheap and dont work well. I disagree, but thats just my opinion.
I dont know how to figure what the minimum size sump for a 140 is, if their is one at all. I can tell you bigger is better. It increases your total water volume, in saltwater this is always a good thing.
Is this you first saltwater setup? Let us know what you got so far and what you plan to keep, this way the users on this site can better help you.
Good Luck, if its you first time in saltwater, you've go a exciting and very rewarding hobby ahead of you.