The Bucelarii:
We can write 100 pages of this issue, but in fact we don't know a lot of these units.
The problem is that these units varies from time to time and it isn't always very clear where these men came from.

Back in history (before our mod IBFD): well known is that Crassus, the collegue of Gaius Caesar, had one of the first Bucelarii units.
These men were garrisoned arround rome and they protected the house and the villas of Crassus. Crassus had a lot of lands and he ned protection. 2500 men total.

To the futute (time at the end of our mod IBFD, and later!):
In the middle and at the end of the 5th century the units of Limitanei and Comitatenses were put together. Also the Comitatenses were reduced to static garrisions.
The future was in the hands of the Bucelarii. The Bucelarii were now the mobile field army. The members of this kind of bucelarii were Isaurians, Thraces, Goths.
The shock cavalry was provided by foederati (german lancers).
The original roman mounted troops (east empire) were the equites sagitarii (regulars like hippo-toxotaii or sagitarii graves).

But what means that for our mod starting in 410?
When a person established a bucelarii army it is well known acc. our sources today that these men were used for a lot of jobs. Conscription (right writing in english??), tax collection, secure the magnates house and fields. These men had swords and sometimes the crossbow.
So you can hire such a unit (hire mercenaries equipt with crossbow) for every important person of the empire like the generals or governours.
So far, so good...

But what about the pedites bucelarii in the game of IBFD?
This is a very difficult question. Aetius for example helped (when he was young) the usuper Ioannes. He had the order to went to the huns and recruit a lot of mounted troops. Well, he did.
After that he came back to italy with thousands of these huns. Also this huns were bucelarii!!

So, if a person tried (a general for example) to found a new bucelarii legion he hired veterans. Perhaps the pedites bucelarii of the mod? I don't know because no book I have can give me an exactly answer.
That means I am not very happy with the solution that the name is "pedites bucelarii" (in our mod). Maybe a better name would be "roman veterans". Pedites Bucelarii means: Bucelarii (bread-eater) soldiers.

The bucelarii of Belisarius for example were Thraces and Goths and huns. In earlier times (but still late antique) I am sure that some generals hired roman veterans. But later they used bad equipt roman milites (like Aetius). These units were fast deployed on the battle field.
A simple example: I establish (like Aetius) a bucelarii army.
I use Goths, Alans, soldiers of some german tribes, huns and veterans.
But all of these soldiers are pedites bucelarii. And that´s what I mean.