I am going to be installing auto meter c2 oil pressure and water temp gauges. Any recommendations on whether or not to put a tee in to use these and the stock sending units for "idiot" lights. If I should, then where do I find the right part to use as a tee. Any advice is appreciated!

 

You can get brass tee fittings at any local hardware store, in the plumbing section.
But in my opinion, keeping an idiot light hooked up is pointless, since the purpose of a gauge is to be able to keep a close eye on how things are doing as they're happening.
An idiot light can sometimes be an "uh-oh it's too late" light.