To start off with, the first issue (concerning item enchantments) is much more important that the heavy/light armor issue! That really needs to be fixed if you want to use this progression.
The heavy/light balance issue I'm referring to is this:
- a typical scale armor goes from +7 (non-magical) to +19(+1feat) throughout the PC's career, for a +13 bonus.
- a typical hide armor goes from +3(+4stat) to +11(+8stat)(+1feat) throughout the PC's career. These options are fairly balanced, they both gain 13AC.
Real tanks can then choose plate armor or a 20 stat, shields, some class features, some paragon paths, or even an epic destiny to further this number, but this is fairly typical for a reasonable investment.
This house-rule would raise the light-armor gain 14AC, which is problematic, because the light/heavy balance is already somewhat precarious. It is already the case that "tanks" have difficulty actually competing with light armor classes for AC, notably, avengers, swordmages and barbarians (particularly post-primal power), get extra boosts as light armor wielders, as do those epic desitnies which grant stat-boosts which is only barely offset by the shield option (which two-weapon defense can compensate anyhow).
In short, I wouldn't touch this precarious balance if I could help it, so hence my suggestion to leave masterwork benefits in place. It's not like "arbitrary" masterwork benefits are any less playable than an "arbitrary" advancement table. So this house rule isn't winning anything, and it's losing in terms of charbuilder interop and WotC support (the more "different" house rules in place, the less likely new WotC stuff is to mesh well with your campaign).
And in any case, armor actually works just fine as-is; unlike attacks and FRW. Hence my suggestion to just hand out expertise for free (perhaps at level 5), and be done with it. Granting an expertise-identical bonus to FRW mostly fixes them too (except the weak NAD, which, well, that's just your weak spot :-D).
So, for almost no balance issues whatsoever, you can get decent progression and stay close to the core rules with a very simple fix: grant +1 to NADs and attacks at levels 5,15, and 25. That's my preference.