In Roman legion, food allotment for a legionare was 2-3 pounds of grains (or flour) and 1 pound of meat and other foodstuffs like Olive, fruit, wine etc. Generally 75-80% grains, 20-25% meat and other components. So you immediately need to quadruple your calculation.
Also, while food was calculated per head, it was distributed by squads. That means that once a week squad leader would go to the quartermaster and receive 1 week of food for 8 people. Then food would be prepared on the fire - meat would be cooked into soup or on open fire. It would not last a week, but after that it would be supplanted with olive, fruit etc, all as addition to porridge or bread or - especially during marches - hardtack. Hardtack needs to be baked, twice at least, for several hours each (preferably more), which requires a lot of firewood. That firewood also needs to be in allotment.
To save on transport space I'd change flour or grains (which soldiers would often ground themselves) to hardtack from the start, as it's easier to transport and it's "condensed". In that case 1 lb of hardtack would be a daily allotment - which reduces the total daily ration by 50%. So, 2 pounds - 1 kilogram - of food (tack, meat, olive oil, wine, vinegar, fruit) would be about right.
As others mentioned, you forgot the other things: food for scout cavalry (horses, depending on unit it would be at least 600), food for oxen, but also Roman legion on the march didn't carry all equipment on the legionare's back. Tents, armor, weapons, ammo for projectile weapons, spares, kitchen utensils, digging tools (to build fortifications for the night, every night), heavy weapons (scorpions, onagers etc, disassembled), fuel for fires (if unavailable on campaing terrain), emergency water rations... This was transported in the baggage train.
Jonathan P. Roth in his book THE LOGISTICS OF THE ROMAN ARMY AT WAR (264 B.C. - A.D. 235) gives the breakdown of nutrition standard and quantities that were required to feed a Roman legionare. In short, it boils down to about 6000kg of food per day. Multiply it by factor of 10 (nominal strength of legion after Aurelian reform is 4800, if double-sized First Cohort then 5200) and for 180 days it's 11k tons of foodstuffs total.
50000 legionares on 180 days of campaign, having their own food for whole campaign with them? Impossible. Baggage train (which was actually mostly mules, with one or two per squad, with only some carts for really big and heavy loads) would be so huge to be be unmanageable - 10k-12k mules carrying squad's equipment alone is a staggering number, let alone added 5.5k ox carts each carrying 2000kg. And this cart max load is a technological limitation; heavy oxen cart would be heavy, made from oak and iron, weighing 1500kg - 2000kg. Thus, 140mm-diameter-double-axed oak cart has per-axle load limit of 1500kg, making it's gross weight no more than 3500kg (subtract 125kg per wheel; they do not count towards axle-load).
Then there's food for mules and oxen, food for slaughter animals... food for oxen for more carts...
Even if moving along rivers, the supply chain must be steady and secured. So quickly force would become smaller, with a lot of detachments to cover supply trains (road or water)...
However. Depending on the region chosen for the concentration before moving to war and how long the expedition will be within it's borders, the baggage train is much smaller, as food can be "delivered" to the places where force will make camps for night.
Then every day the baggage train will be smaller, because you can use oxen for meat - and they will be slaughtered when needed, and in the meantime you can use them as spares, then effectively doubling the daily mileage (at some point, initially it will be as slow as one expect).
You could alleviate a lot of those issues if you choose a objective relatively close to your borders and you make it a defensive, fortified position, thereby allowing for reduction of the daily ration by anything between 25%-50%. Combined with combat losses you could get away with halving the baggage train, which sounds impressive, but going from 8000 carts and 10000 mules to 4000 carts and 5000 mules does not help much...