Hal, I have just a few comments.
(1) just finished installing two, one-eighty-degree 18" radius curves on my layout, and one of them has a significant issue at the join between two pieces of flex track. It's REALLY hard to get a good smooth curve through a flex track join, and especially hard at 18".
(2) For that reason, I would seriously think about using Kato Unitrack for those long (180 degree) curves: flex track will require a join right in the middle. You can easily transition from Unitrack to flextrack (I think Kato even sells a transition piece.) This will insure trouble free operation through those long curves.
(3) If you decide to go with flex track, solder the joins before you curve the track and before you lay the curve. I don't know if this will solve the problem I had, but it sure can't make it worse. The earlier comment about ribbonrail is spot on. I personally prefer Atlas code 83 flex track: I think it flexes more smoothly.
(4) Your 22" radius plus 1.5" to the edge of the right-of-way means your trains will be running VERY close to the edge of a 48" sheet. You'll have no room for scenery and nothing to catch equipment in the event of a derailment. Add to that the long reach issues, which I think you may be underestimating. I'm 6'-2" and it was about all I could do to reach the back of my 32" wide layout. It's one thing to reach four feet across a flat table; it's another thing entirely to reach across a 4 foot layout with trees, structures, scenery, etc. (By the way, I have a BLI 2-8-2, a Genesis 4-6-6-4, and a Proto 2000 2-8-8-2. All track nicely around the 18" radius - except at those pesky rail joins! - although the articulated locomotives look a little stupid hanging off the centers of the 18" curves. (I plan one day - when I get management approval for my next expansion - to replace those 18" radius curves with 24".
(5) Last (and this is just my personal experience and may be entirely out of date), I have in the past bought two Bachmann DCC locomotives, and neither one has ever performed acceptably. No low speed performance at all; high speed performance is not at all smooth or consistent. This experience is years old and may no longer be relevant.
Good luck!