What was the structure of a Sengoku-Edo period army?

[the great yuan khan]

I'm writing a historical fiction story about a samurai who commands a contingient of men(ashigaru and samurai) during an invasion of a nearby country. Did they have modern structure such as platoons, units, batallions, and divisions? I want to know the structures of their armies at the time so the reader has a clear understanding of how many men he's in charge of. Did samurai at the time have ranks as well? In my story, the samurai is a ronin who used to be a high ranking samurai until his lord was killed in Sekigahara. He's been given redemption by commanding said contingent of soldiers because of how well he commanded his men in Korea.

[Solanum]

A daimyô's retainers were expected to provide men for war, and this requirement often formed the basis of a daimyo's military organization.
Landed warrior-houses had to provide a set number of horsemen. We may assume that the retainers were also expected to bring with them a certain number of footmen per horseman, though this is not mentioned specifically. There was no universal system of recruitment or organization among the various daimyô - methods were adopted and implemented based on local factors, resources, and the strategies of individual daimyô. To present a case in point, the following is an order issued by the Shimazu daimyô in 1578 calling men up for service to fight the Ôtomo:
Shimazu mobilization order 1578
"Holders of 1 cho: 2 men, master and follower; the master's service shall be personal;
holders of 2 cho: 3 men, master and followers;
holders of 3 cho: 4 men, master and followers;
holders of 4 cho: 5 men, master and followers;
holders of 5 cho: 6 men, master and followers;
holders of 6 cho: 7 men, master and followers;
holders of 7 cho: 8 men, master and followers;
holders of 8 cho: 9 men, master and followers;
holders of 9 cho: 10 men, master and followers;
holders of 10 cho: 11 men, master and followers;
"The foregoing is the assessment [based upon that] for one cho of ta (Meaning more than one cho and less than two). The military service from 10 cho up to 100 cho and 1,000 cho, [shall be performed on the same basis]. It should be under- stood that armor (gusoku) is assessed at the rate of one set for one cho."
Note: One cho was equal to about 2.94 acres of land; this was reduced to 2.45 acres in 1594.

[the great yuan khan]

Is it the same structure as a national army? The setting of the story takes place during the edo period when the whole country is united.

[Solanum]

There are no "national" army. Almost all army are private, units in the modern sense of the word did not exist before Meiji period, though the personal retainers of a given general might make a name for themselves. Lesser lords maintained their own contingent but could be moved about within the order of battle (that is, from the personal command of a high ranking lord to another) as needed.

[Solanum]

Shimazu recruitment order 1576
'Assignment [of service] for the expedition:
Those [holding] one cho of ta: one man per cho, [meaning] two men, master and follower; providing their own rice for food. Besides, one attendant laborer (tsumefu) shall be provided by the churches and temples; 3 draught horses shall be assessed upon churches and temples.

Next, the implements to be carried:
1 tekabushi (?), height 3 1/2 shaku, width 2 1/2 shaku
1 log, 6 shaku long;
1 hoe 1 broad-axe 1 sickle
1 saw 1 chisel 1 adze
1 dirt-carrier 1 coil of rope.
Those [holding more than] 2 cho: one man per cho, [meaning] three men, master and followers; providing their own rice for food. 2 draught horses shall be assessed upon churches and temples, as well as widows.
The aforesaid implements for work (fu-shin) shall be carried into the camps at the rate stated above for each cho of ta.

Up to 100 cho and 1,000 cho, the assessments shall be [the proportionate multiples of that for] one cho of ta. Those who have no land (muashi-shu) shall provide between two of them one attendant laborer (tsumefu) being assessed [also?] upon churches and temples, and widows; rice for food to be their own provision. 3 draught horses shall be provided likewise by churches and temples.
For thirty days during the expedition the rice for food shall be self-support; beyond thirty days, it will be provided by the authorities (kogi). Those [holding ta] between five and nine tan shall provide their own rice for food; those between one and four tan shall receive rice for food from the authorities.
Tensho 4 y. 8 m. 1 d. [24 August 1576]'.

[Solanum]

Shimazu preparations for the Korean Invasion, 1591

For those owned 1,020 koku; 95 retainers in all.
Total, 3,230 men of this class, being 34 men with each [retainer] (zhin-tai).
For those owned 510 koku; 24 retainers in all.
Total, 408 men of this class, being 17 men with each [retainer].
For those owned 300 koku; 143 retainers in all.
Total, 1,430 men, being 10 men with each [retainer].
300 squires on foot. 900 laborers (fu-maru), being three laborers with each
[squire].
For those landless(mu-ashi) men; 500 in all. 1,000 laborers, being 2 laborers with each [land-
less man].
665 carriers of weapons(do-gu).
2,000 laborers from the lord's domains(kura-iri).
2,000 boatmen.

Grand total, 12,433 men.

Provision for these men for five months, 10,522.9 koku, inclusive of supplies
for boatmen and their chiefs.
272 horses. Their provisions 616 koku of beans, being for five months, at the
rate of 2 sho per day [for each horse].
Rice and beans together 11,438.9 koku.

The lord's own army:
[Shimazu Yukihisa's] 9 mounted retainers, with 332 men.
[Ijuin Tadamune's] 69 mounted retainers, with 2,332 men.
Total, 350 mounted retainers;

Grand total, 15,097 men.