When deploying a Terminal Server environment there are a few very important steps to consider. Hardware, Licensing type, Operating System, Is it going to be virtualized? User Profile Locations, System Lockdown.
At a minimum make sure you have a dual core CPU. This will perform better than any single core processor. With regards to memory I would ensure you have at least 64mb per user but the more you have then the better performance. If you are going to be using CAD apps and other memory hungry programs then consider bumping the memory up to a level you feel comfortable with. Later on in this article I will publish a link to the Microsoft Whitepaper on Capacity Planning. This will give you a list of scenarios to help you plan your deployment.
I wouldn't scrimp on the server resources at this stage as it may cause you problems in the future if you have planned growth or not. You may find in a few months that you need to run another application on the Server, What are the consequences of this, plan for it now so you don't have to in the future. Nothing is bullet proof but the more groundwork you do now then the smoother the deployment and running of the system will go.
RDS licences come in two flavours, Device and User. Consider at the pre deployment stage exactly what licences you will require as it will be very difficult for you to change once they have been deployed. Per User licences basically give you one licence per user. This is handy if you have roaming users or users who access the terminal server from multiple devices. Per Device licences means that each device that connects to the terminal server will require a licence. This is the best option if you have workers that work shifts and multiple users use the same device. Consider the following. You have 100 shift users but only 50 devices. In this option you would select the device licensee's option as the devices will be shared. More information about licensing can be found at the following Microsoft TechNet https://technet.microsoft.com/en-us/library/dd262138(v=ws.10).aspx
The OS you deploy is going to be dependent on the business applications you are running. Wilts Microsoft product are generally backward compatible. May applications supplied by third parties may not work the way they are intended on newer versions of MS operating systems. Always check with providers about the Hardware and OS requirements before deploying your TS. If you are going to be deploying a new TS environment with just the more common application like office or adobe programs I would consider going for the latest RDS OS (2012 at time of writing). Your users are going to be more familiar with the layout and you are not going to have the nightmare of licensing downgrade. Believe me downgrading 2012 licences to 2008r2 is a feat in itself. Unless you have the correct contact. ( email me if you need them!!)
If your business has a need for 24/7 operations then always create a good backup/DR plan before you deploy. Consider two terminal servers where you could not only move users from one to the other in case of a failure but you could also load balance users for better server performance. This hands down is my preferred option as it gives you a much faster way of getting users back up and running into his event of a catastrophe. You could virtualise your terminal server giving you the option of moving the Virtual server to another Physical host in the event of a failure. This would require a second Physical host machine. A good option if you have a lot of servers that can be virtualized. Just take into account that these machines will need to be fairly high performance, not just cup and memory but also network interfaces. The last thing you want is a bottleneck. Also consider a SAN if you are going to have virtualised servers, Central storage configured and managed the correct way will be a big benefit in both recovery times and network performance.
Depending on the raid configuration of your new server and the hard drive partitioning you may want to consider where you are going to be storing all the data required for your users. If your disk has been partitioned to allocate only 35-40 GB to the c: / drive then consider storing all your applications and user profiles on a secondary partition of drive. You don't want to run out of space on the main OS drive as this will cause the server to stop operating.
If you don't apply some kind of plan to stop users carrying out task the responsibility of the administrator then you will run in to problems. Think about updates, you don't want everyone installing updates and rebooting the server as and when, you also don't want users to be able to install programs or shutdown the server unwittingly. Apply Group Polices or amend registry entries before you allow anyone to log on to your newly deployed server.