Hi all, I am still pretty green when it comes to casting and fly fishing.
My favorite few creeks (from spin fishing) are really dense and thick, which makes a short rod, like a 6ft 3 or 4 wt, very appealing.
I've heard they can be significantly harder to cast than the standard 9 foot 5 wt.
Should I focus on larger and more open streams to practice on an easier rod? Would a 6 ft rod be biting off more than I can chew?

If you're using it on small water and making short casts I think you should be fine. Roll casts are only a little trickier with a short rod. I have a short 3wt and like it. Unless I'm fishing lakes and need real long casts, then I struggle a bit.

Back in the day, my Buddy and I would travel to the mountains around Somerset, PA to catch a few native brookies. I had a Fenwick 6 foot glass rod saddled with a Pflueger Medalist 1492 reel spooled with a No.3 line. We had to use short rods because of the jungle like over growth. We caught many but kept a few for our "shore" lunch. He would break out his Sterno stove and a stick of butter and I would get the Iron City from my backpack. Those were great days and fond memories. Loved the rod/reel combo, but sold it a few years back. I'm 72 with lung disease and just can't do it anymore.
 

Fly rods on both end of the spectrum take a little time getting used to them.  A little 6' 2wt on a native stream is hard to beat.  You will figure it out, and once you do, you will have one more trick up your sleeve.  

Thanks useful tips