Well, my armies tend to be pretty lightweight for Rome too, but it works. Besides, the losses are easier to replace. And I managed to get 8 "roman" units to glod chevrons - the most experienced army I've ever commanded.

So, down to numbers:

1 gen: I only tend to have one "proper" army in the field and, if it is a war of conquest, then another stack of "garrison" troops, but this would be my best (read most promising) general

2 accensi: cheapo llight troops for taking of enemy's skirmishers.
2 Boatroas (northern archers): same job as the accensi, usually a bit more specialised.

3 hastati: with 1 golden chevron each. As I said this is my core army.
4 princies: some with 1 , one with 2 gold chevrons. If they can't do it, its hopeless.
2 triarii: both have 1 golden chevron although I don't use them extensively.

1 equites: 2 golden chevrons too. These guys alone have broken Gaesatae. Which is no small thing.

Then there are usually a couple of units of Lugoas, to do the sapping, push rams, absorb charges, etc. These are recruited for each campaign and are not a part of the standing army.

1 Leuce Epos: Well... they are not fantastic but come handy from time to time, and they are usually so massacred after a campaign I just disband them.

The last 3 units depend on who am I fighting. For instance, after I conquered Sicily I tend to fill them with Lybian infantry as they are pretty solid troops good for supporting my infantry and storming walls even. Usually though, for my northern campaigns I use heavy barbarian ingantry, with pretty much the same purpose, storming walls, charging the flanks, etc.

I reckon I probably got close to that 50% ratio for Roman-non roman units... Whaddaya think?