Wow. Thats a lot of reading. I didnt know if I was going to make it through it all or not.
Ok, it looks like you are on track so far with radio 3.42.30 but keep in mind radio 3.42.50 is out and available on the boards.
When you do boot regularly, what are the numbers right below the radio numbers? Thats your ROM version BTW.
Olipro 2.4 is where you want to be so your good so far there too.
You said ( in paragraph 8 ) that you "then went and downloaded what I thought was the latest stock ROM from Sprint". You dont want a Sprint ROM on your phone but just the radio. You will cook your own ROM.
While you are in the rainbow screen, if you connect the USB cable does it change from Serial to USB? If so, then all you need to do is go and download BuildOS and cook your ROM. Once the ROM is finished building you would have to put your device in BL mode or it will force it there anyway so you are not far off at all.
However, if you want to get out of BL mode to have the device be able to sync again then just have it connected to the PC is USB and go to C:\ttn240mfg and click on titan_exitbl.exe which is just what the name of the file implies, the Titan Exit BootLoader.