Starting Saltwater

Welcome to SW! What kind of tank are you wanting to do? Fish only with live rock or a reef?

I think the 65g tank would be great and I wish I could have started with a larger tank like that.

I'm not familiar with Southdown Play Sand. Make sure it isn't a silica sand. You will want to use an Aragonite sand probably for the best results.

I love live rock and it is great fun to pick out the pieces you want. You are going to want at least a minimum of 1lb per gallon of water. Probably more if you are going to do a reef.

If you are doing a reef, you'll most likely need to upgrade your lighting. Corals need more light than a typical fluorescent fixture will provide. If just doing fish with live rock, a standard fixture should be fine.

There are lots of choices of salt for your tank. I'm still reading about what I will use eventually. Right now I'm using Instant Ocean and I have happy snails and crabs.

You shouldn't need the Prime.

I can't help any with the skimmer as I'm not currently using one. You will however want to probably get a powerhead for the tank to keep the water moving.

I purchase my RO water at the LFS. I hope to have my own unit in the future.

For all of you that are more knowledgable than me...remember I'm a newbit, please correct me on the above if I'm wrong.

Just remember that the thing you will need most is patience. Nothing good in this hobby seems to happen fast, but trust me, bad stuff happens faster than you can believe.

Do NOT get that Prizm skimmer. Seriously it is horrid. If you must have a HOB skimmer try a Aqua C Remora or a Octopus. Deltec is nice but pricey. If you have a sump even better your options for skimmers get even better.

You can get any live rock you want really. Look for pieces that aren't real dense. Marshall Island Rock is beautiful but more expensive. Premium Fiji is an affordable nice rock.

You can use the Southdown but I opted for aragonite and even those with Southdown opt to have it under aragonite it seems.

I agree with Tiki that you'll want to upgrade the lights but if you're just going to have fish to start you can wait and investigate what you want to add to your tank. Some corals and inverts take higher light than others. I thought I'd stay away from the SPS and clams and go for T5s but when I found a great deal on metal halides I didn't look back.

In addition to your list you're going to want:

powerheads (go for 10-25 turn over for a FOWLER)
thermometer
think about a sump/refugium but it can be added layer
test kits (ammonia, nitrate, nitrite, pH, phosphate, alkalinity, copper) Then as your add to your tank you'll want to test for other things too.
RO/DI is a good idea.

This site is a good base for information and I find it friendlier than most towards newbies. I'd get familiar with the articles here, the stickies on top of the newbie marine forum. Check into Robert Fenner's book The Conscientious Marine Aquarist, bookmark his site wetwebmedia.com and read, read, and read some more.