I know I sound like a broken record - but test cast as many rods as you can before buying. A good fly shop can help.
“What length should I be looking for?”
Length – 9’ minimum, a 91/2 or 10’ may be better but may not available in all the rods you listed.
The problem that I see is that in Saltwater fishing, you will need to do a lot of double hauling for distance casting, and casting in the wind. A fast action rod would be more suitable for that type of fishing. While for steelhead, a slower action rod that flexes to the butt is most useful for casting (flinging) weight, and to wear down a big fish on without breaking a relatively light tippet.
“Now for more specific brands. I was looking at the St. Croix Avid 9'6" 8WT, 4 piece (A968.4), Orvis Clearwater II 10' 8WT, 4 piece (Clearwater II 108-4), TFO 9' 8WT, 4 piece (TFO 8904X). G Loomis is a bit out of my price range. It looks like the Sage rods that are in my price range have a wood reel seat. I've read that you would need anonized aluminum for the reel seat. If I'm wrong, please let me know.”
Since the “CFO” won’t let you spring for two rods, I would select a rod that is fairly fast. IMO, you can get away with a faster rod for steelhead (I’ve caught tons of steelhead on my Sage RPL 8wt), but a full flex rod is a true handicap for casting for distance and in the wind wheen SW fishing. BTW, the Sage rod in an 8wt does not have a wooden reel seat insert.
All decent rods:
SC Avid – Moderately fast
Sage Launch – Moderately fast
TFO TiCr – Moderately faster
TFO TiCrX – Pretty darn fast
Orvis Clearwater II - ?????? new rod - heard good things about it, but it may be on the slow side for SW.
“What about Cabela's Stowaway 9' 8WT, 7 Piece or Orvis' Frequent Flyer 9' 8WT, 7 piece? If I went with these two choices, should I go one weight higher?”
Both rods are fairly slow action and would not be the best choice for saltwater fishing.
Try to cast them all if you can. In my hand I believe the TFO’s would probably cast best for distance. Good luck.
PS - I believe that all the above rods in an 8wt have a fighting butt. DO NOT buy a rod for salt or steel without a fighting butt - that will become obvious as soon as you hook up and are taken for a ride!