Hi Frozen,
Welcome to F-Class. I'm one of the guys who worked hard to get F-Class accepted in MN about 20 years ago. I ran a weekly league in Elk River for years, getting about 40-50 new shooters into the sport each year. My suggestion to new shooters is first to decide F-Open or TR?
You've got a couple rifles ready for TR already. A 1-8" 223 is perfect to learn wind reading skills. 80 and 80.5 grain Bergers shoot great. 155 to 200 grain bullets in the 308. The 223 hits the easy button as less powder, less recoil for 88 shot days. I shot 308 for years and was usually beat by 223 guys.
F-Open is another world completely. The 6BR and now with the availability of factory brass for variants gets the easy answer. 105's shoot great, long barrel life. I love the 284 and especially the Shehane variant. The 284's with 180 grain Bergers shine best at 1000, and windy days at 600 over the 6's. If you're looking to rebarrel one of the 308's, the 284 is an easy path since you already load for it.
I had many guys show up with 7 WSM, Rem Mags, 300 Win and RUM rifles over the years. 22 shots in one night was enough for them and they found other rifles quickly.
Pick up a NF BR in 12-42X with a NP-2DD reticle, used around $1000 on this forum and you'll be set! FFP doesn't work well on a small target.
Good Luck and enjoy!
Scott