genesis, I think you have a sound plan. I have both of these models, and I'd recommend the G23 over the G27 as I think the compact is a bit more versatile than the sub-compact, and the recoil is more noticeable in the baby Glock (not painful or anything like that; however, quickly-fired but accurate followup shots WILL be slower with the G27). Glock does offer an adjustable rear sight, but it's fairly crappy (remember, this is coming from a big fan of Glocks), so buying a decent aftermarket sight is a better way to go.
Be aware that the less-expensive conversion kits have lightweight (aluminum?) slides, and so the weight/balance of most converted-to-rimfire Glocks are completely different than the centerfire versions. A newer conversion kit with a steel slide is now being made, but I think it is a bit more expensive than what you listed, and you have to use full-power high-quality .22 ammo to get good reliability.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)