Do I have to re-install all of my software that was previously installed on Mountain Lion onto OSX Mavericks?

If you are upgrading an existing system, then the only software affected is OS X. All other files are left in place untouched. Some of that software may require updating for Mavericks compatibility. You also need to be sure all your hardware meet the Mavericks requirements.

Upgrading to Mavericks

You can upgrade to Mavericks from Lion or directly from Snow Leopard. Mavericks can be downloaded from the Mac App Store for FREE.

Upgrading to Mavericks

To upgrade to Mavericks you must have Snow Leopard 10.6.8 or Lion installed. Download Mavericks from the App Store. Sign in using your Apple ID. Mavericks is free. The file is quite large, over 5 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.

OS X Mavericks- System Requirements

Macs that can be upgraded to OS X Mavericks

1. iMac (Mid 2007 or newer) - Model Identifier 7,1 or later

2. MacBook (Late 2008 Aluminum, or Early 2009 or newer) - Model Identifier 5,1 or later

3. MacBook Pro (Mid/Late 2007 or newer) - Model Identifier 3,1 or later

4. MacBook Air (Late 2008 or newer) - Model Identifier 2,1 or later

5. Mac mini (Early 2009 or newer) - Model Identifier 3,1 or later

6. Mac Pro (Early 2008 or newer) - Model Identifier 3,1 or later

7. Xserve (Early 2009) - Model Identifier 3,1 or later

To find the model identifier open System Profiler in the Utilities folder. It's displayed in the panel on the right.

Are my applications compatible?

See App Compatibility Table - RoaringApps.

I suggest you create a clone backup in addition to your Time Machine backup. Once you have upgraded it's very difficult to revert if there are issues. With a clone you simply boot back into the clone and you are right were you were before upgrading.

Both of these applications can be used to create a clone.

SuperDuper! http://www.shirt-pocket.com/

CCC http://www.bombich.com/download.html

Installing Mavericks will not erase those things unless you choose to erase the disk first.

However, some developers are overbearingly afraid of piracy, and their software will often "break" because they "sense" that have been moved. Those you will have to reinstall.