I would say the 1000 device count might be over the next 12-18 months - hard to say as the company is constantly looking at consolidating offices, as well as possible expansion into new regions.
We are currently at 182 controllers, 360-370 APs and a handful of RAP2 devices.
Initial deployment was with the "wireless as luxury" mindset. As the tablet market and BYOD trend exploded, I've already told them that we realistically need to double, if not triple, the number of APs. Standard response is "not going to happen."
Short term goal is to add around 1 AP per office this year - that would be 180 minus however many offices I've already completed, so probably 100-150. I have some offices that are small enough that they won't need any, and some that I'm taking from 2 APs up to 6. Given the slowness of getting purchases approved, and relying on vendors to do the installs, I'm probably limited to 6-8 offices per month.
Long term - ??? The company could expand and make some acquistions and basically double in size, in which case I'd be looking at 1500 devices.
Any new server recommendation from me will be for at least 1000 devices, with a strong push for the 1500 settings. I believe the recommendations for 1000 devices will meet the "minimum" for 1500. Storage and RAM is pretty cheap these days.
I guess my main concern is I'm already experiencing 10 second delays when switching tabs in Airwave. Each version upgrade seems to be make it slightly worse. If my next upgrade step is going to require a system backup, wipe and reload of OS and app, and import of the backup, now would be the best time to look at a new server if needed.
If there were any issues with the upgrade, I'd still have the old server to bring back online. Assuming no issues, I would then look at using the old server as a possible failover (assuming data center doesn't repurpose).