I certainly mean you no disrespect, or shortness, but it seems, from your question that you basically seek a "one size fits all" solution to your fly fishing needs. In my 4 1/2 decades of experience, I have not found such! Having said that, here is my answer to your question(s) ....
1) Your 9 ft rod is/will be/should be GREAT, assuming that you are not a so-called "expert" fly caster/fisherman, and you are fishing from/onto fairly "open" waters, like lakes, rivers, streams, etc. with fairly unlimited backcast & forecast areas. These could include fishing from a boat, fairly/reasonably brush/tree clear banks, etc. If you primarily fish in "tight" areas, like brush & tree filled banks of smaller streams, you would then be better served with a much shorter rod which would also necessitate more expertise and practice with same.
2) Your selection of #8wt. is what I would consider to be truly IDEAL for largemouth bass, particularly if you fish in an area where you can realistically expect to hook/catch "monsters" in the 5 pound (and up) size range. As far as smallmouth bass, bluegill, & trout go, I sincerely believe that an 8wt. outfit is gross overkill, and will "spook" more fish than it will catch.
3) For bluegill/bream, and "normal" or "smallish" sized trout, I use (and recommend that you use) a 4wt fly fishing rod & reel outfit. For "medium" sized trout, and a day of bluegill/bream fishing, a 6wt outfit would, in my opinion, be appropriate, given appropriately sized leaders, flies, etc.
4) I currently own/use both 4lb and 6 lb rod(s) and reel(s), spooled with WF-F line, and appropriate backing and leaders. I am in the process of researching (and buying) an 8lb outfit for my (hopefully) huge bass adventures. I prefer the "F" line, as opposed to a sinking line, except in/on specific locations/waters. I find it to be lighter, produces less "line slap" upon the water surface when cast, and generally better overall, assuming that your quarry are feeding on the surface.
IN SUMMARY, by ALL means, KEEP your 8 weight outfit, but I would suggest that you "relegate" it primarily to "industrial size(d)" bass fishing. Get yourself a "lighter" outfit, of either 4 weight or 6 weight, or preferably BOTH, for your smaller/lighter weight fish, particularly bluegill/bream, and most of the commonly found (and caught) trout.
If you found a mouse running through your kitchen one night, you certainly would not "call in" an "air strike", or a tank or artillary bombardment. A simple mouse trap, or maybe a .22 would be more than enough. The exact same thing applies to fly fishing - so don't "nuke 'em" with overkill - rather, match your equipment to the quarry at hand, and enjoy successful & enjoyable fly fishing for the rest of your life!
PS - Please do NOT "scrimp" or "be/get cheap" on your selection of fly line(s). Doing so will NOT serve you well, at all. I know it sounds foolish to buy an $80.00 "complete" fly outfit, and then spool it with $70.00 fly line, plus the added cost/expense of backing, leaders, flies, etc. Buy the BEST that is available, for your needs, and fish well. If you are unsure, the knowledgeable folks at Bass Pro can help/assist you in this serious decision making process.
CATCH LOTS, ENJOY IT ALL, and I hope that this has been a "little bit" helpful to you in your quest to "catch 'em all" !!