Kegging question

I just bought my kegging supplies. Just a picnic tap for the moment with 5lb tank. The guy at the beer store told me to hook up gas to my beer out line when first carbing because of the tube that goes to the bottom (helps get CO2 into beer better?)...and then after it is carbed switch them back to the way they should be....Is this good practice?
Any other tips besides checking for leaks for a first timer?

You can do that...HOWEVER the grey gas connect is not the same as the black beer connect. You'd have to put a black connector on your gas line.

Honestly, I don't see a need unless the beer is already aged (i.e. not green and therefore ready to drink) and you need something carb'd fast. Even then you can just connect the gas to the In post, set to 30psi, and rock the keg for an hour to fast carb it.

There's a lot of tricks to fast carbing, but as a beginner to kegging I'd keep it simple. Set the psi to 10-12, connect to the In post, and wait 10-14 days. It'll be carb'd at that point without being over-carbed, and no fussing around.

yeah I plan on doing the set it and forget it method....as I am not in a hurry on this keg.

They didnt inform me on t hat that I would have to switch the quick connection pieces. I didnt know they were different either, what is different about them?

They are slightly different sizes. Not a large enough difference to see visually but you quickly realize it when you try to jamb one on the larger post and it gets stuck. It's a common mistake that I made just to see what would happen.

But if you're just hooking up the gas, you don't need to connect anything to the "in" connector. Obviously you're not going to be tapping the beer while pumping CO2 into the "out" connector.

If I just do it with the gas line in as i am carbing does it matter if you have anything hooked up to the beer out?
Can I just leave the post with nothing on it, or is it better to have the picnic tap hooked up, or just the quickconnect piece on, does it not matter?

No, you don't need anything hooked up to the beer out post while carbing. You CAN, but it's not needed.