I know that I should probably ask Barracuda sales but would it be good to get a higher model that supports 1000 clients? Or should I just stick to my needs which is the model that supports 500 clients?
Because it is something that you will have for a number of years I would suggest speaking to your management and seeing what their projected growth is for the business for the next few years and then base your requirements around that.
If storage is the only reason to look at the higher models don't forget that you can add in extra storage yourself either via local disks or network based storage (the lower models can access it via SMB, the higher end ones can use iSCSI too as an option).
