time capsule question

Yes, you can use time capsule in Medium size network, my personal suggestion in less the 20.

Upto 10 Mac Device can be used to back up in time capsule.

Time Capsule doubles as a full-featured AirPort Extreme 802.11n. So, if you’re adding Time Capsule to an existing wireless network, you’ll want to set it as your primary base station, rather than as a network client. That way, you benefit from its faster performance and ensure that your backups occur without any speed bumps.
Use AirPort Utility 5.3 or later, included with the Time Capsule or available via Apple Software Updates or from Apple Support Downloads, to set up your Time Capsule.

To set up follow the following steps:

Connect your Cable/DSL (broadband) modem to the WAN port of your Time Capsule via an Ethernet cable.
Connect the Time Capsule's power cable to an AC outlet.
Open the AirPort Utility. which is located in the Utilities folder, within the Applications folder (/Applications/Utilities).
The Time Capsule will have an initial name such as "Time Capsule fea88c". Click continue to proceed.
Select "Create a new wireless network" and click Continue.
Follow the rest of the on-screen instructions. When finished, your Time Capsule will restart and apply your settings.


Guide: https://manuals.info.apple.com/MANUALS/1000/MA1645/en_US/airport_time_capsule_80211ac_setup.pdf

please read my question again.

if I add a time capsule to an existing medium size network, would it cause issues on the network. :

NO problem you can add it, but set it as your primary base station, rather than as a network client. That way, you benefit from its faster performance and ensure that your backups occur without any speed bumps.

it is just temporary for today to sync my directors devices to it so when he takes it home it will automatically sync:

I understand that this Time capsule is going to be used at home then, suggest to do it as independent net work only connect the lan cable right now to it so it can be used in current new work.