Catch can, 85mmTB, Intune and voltage stabilizer / grounding kit are all effective upgrades, very easy to install, and no special skills or tools are needed.
So, first thing to get is a Catch can for a Hemi. Not only keeps the intake and TB clean, it will run better too. Without one, the unburnt hydrocarbons are fed back into the combustion chamber, effectively lowering the octane number and the ECU will retard timing under load to avoid pre detonation.
The Modern Muscle taper ported 85mm TB is a worthwhile upgrade, 4 bolts to install, about a 20 minute job. Removing / installing the intake takes longer than putting the TB on.
When you get an Intune, get a CMR custom tune as the Diablo canned tunes don't do much. Sean at Hemifever will sell you the Intune and the CMR tuning, so you datalog, send him parameters and he will update with every mod at no added cost for as long as you own it.
The stock intake works great; I removed my CAI after testing it with the stock and the 85mm TB, and with the stock airbox torque and drivability is much better with both TB's.
I also had a Magnaflow and couldn't stand the noise, so put the stock exhaust back on. Low end torque is better, so the throttle responds instantly witbhout having to rev the motor. It is also MUCH quieter, no droning and I like it being fast and stealthy, i.e. can get on the throttle and it really goes, without drawing attention.
MPG improves with all these, that is, if you keep your foot out of it.... it is so much more responsive that my go pedal is applied more frequently, so city mpg is about 12, but with a big smile
Hope that helps, and good luck !