I plan to use time capsule as a file server into a production environment with 3-4 mac clients.
Can you give me some information about possible drawback with this choice? What are Time Capsule performance?
The drive is a nice, fast server grade drive but the controller is underpowered to be a NAS for professional video work.
That being said, even with two people reading / writing lots of small files, the Time Capsule works surprisingly well. At times when 3 or more people are hitting the drive at the same time for small IO, you will certainly see a slow down. Much more so than on a real NAS or server that has RAM to cache the filesystem and not be limited to the physical disk access.
So if the usage is low or you are on a tight budget, have at it!
Do be sure to have one of your clients be responsible for backing up all data stored on that volume since most backup solutions do not read from a Time Capsule directly. Using the built in clone tool is not at all optimal for production use, but is fine to make a snapshot over night or over a weekend when you have occasional cause to snapshot the data.
As bmike stated, backup of the Time Capsule is an issue. My advice is that you'd be better off using a NAS with RAID 1 or 5 and swappable drives so that you're not going to lose data.
For the cost of a Time Capsule, you could build a relatively good FreeNAS box, or buy an off the shelf NAS which both support AFP and will work happily with both OSX and Windows systems.
You'll get much more control over access rights with a dedicated NAS solution, and with RAID you get more redundancy in case of drive failures. Backup of NAS drives to other NAS' or external drives is also normally an out of the box option too.