Sean
You are well on your way!
If you want to do an Op Telic Challenger then you don't need the Accurate Armour conversion. The AA Conversion was for the Trumpeter Challenger 2 kit which did not include the Desertize uparmoured parts. You have the Tamiya Desertized kit, you're good to go!
The Lionmarc barrel is good I have one, but read the following review to make up your own mind if you want to get it. Some people say it's great others don't care for it. The one thing that stands out is the rubber shroud over the barrel near the mantlet, the lionmarc sags the Tamiya is straight... this part looks like an accordion.
http://www.perthmilitarymodelling.com/reviews/vehicles/lionmarc/aw20000.htm Also, there are loads of decals out there for Op Telic, you've mentioned 2 but Echelon also carries a set as well. Might be worth checking them out as well.
Other then that, there is a section on how to apply the Rustoleum textured spray in the book Modelling the Challenger tank which you have. For masking reference on where NOT to spray the anti slip surface check our Prime Portal, the modelling book you have and the article I emailed you a while back. They are priceless!
Also, if you don't like the headlights in the kit, and you're having a hard time finding Grief Lights, try looking for MV Lenses, they are used in model rail road modelling, they come in a variety of sizes.
I also just picked up the Bronco Tracks... hobbyeasy.com sells them for $9.96 CDN... which is pretty close to USD these days... add a little for shipping and you're set! These tracks rock!!