Some people have shown the Ninja Regs to be more consistent than the Myth regs. The Myth regs are nice for the Tibs just because they are physically shorter so give you a wider range of adjustment if using the tank in stock combo. Personally, I prefer the pressure adjustable Ninja to offer the best from a performance perspective.
Someone testing Rifled barrel consistency found that the super high pressure output Ninja reg gives a more consistent shot with the rifled barrel (More info can be found on MCB). We've also found anecdotal evidence that lowering the input pressure slightly (from 800psi down to 600psi) causes an improvement in consistency with the rifled barrel. What I've gleaned from both of these tests is that the internal marker regulator has ranges that work better than others for consistency. You may need to experiment with the ninja tank pressures till you find which works best for you.
For upgrades, there really isn't a whole lot to change with the internals for Tiberius markers. About the only thing you can do is polish the bolt and power tube (or send it off to someone to do).
As to the barrel cleaning, I just run hot water, then a fluffy squeegee or shotgun barrel cleaner through it to remove the residue left by first strikes. The residue starts to build up and needs a cleaning after 50-100 shots. I know some prefer cleaner solutions, I'll let them chime in with brands.
Eclipse Drops or Gold Cup Oil for oil.
If you prefer lube the only one "ok" by Tiberius is Tech T Lube and only if running compressed air. Oil seems the preferred, but if you have to use lube I thought I'd mention it.
There are a number of online vendors that sell the mags for $29.99