About the patch.exe in the fpc/bin directory., It is (at least last time I checked) very sensitive to the correct line ending (windows vs unix style). I don't recall which one it wanted, but if you got the wrong one, it may just crash. In that case an editor like notepad++ which can convert the file will help.
You can (and probably should) install 2 Lazarus in parallel). Before going to use SVN, why not trying a snapshot.
However, if you use more than one lazarus, there is one thing you MUST learn.
Use the --primary-config-path=c:\some\folder\ option. Under windows in order to start lazarus with this option, you must create a shortcut, and edit the command line in its properties. Then always use the shortcut to start lazarus.
Otherwise you will share the same package between both lazarus versions, and latest when you install a package, you will be in trouble.
Both lazarus can use the same fpc installation => your 2nd lazarus can use the fpc that is within the 1st lazarus install dir.
But: you must never move or rename the fpc folder. Because fpc.cfg (which is in the fpc dir) contains absolute pathes)
If you install 3rd party packages, you can only share them between installations, if both lazarus are using the same fpc. To be save, install each 3rd party twice.
Once that is mastered it is a very small step to use svn.