The EVO is not supported for CM9 by the cyanogenmod team. You will have to get an unofficial port from XDA
[ROM] Unofficial CM10 for Supersonic Nightlies **Built from source **Alpha - xda-developers [ROM] Unofficial CM9 for Supersonic Nightlies - xda-developers [ROM] [LOTK] CM9 PS Style (8/1/12) - xda-developers
you have to partition your card and then upgrade to ext 3 or ext 4. it is all done in recovery. it is not necessary, but the instructions is if you want to move the apps entirely to the sd card. it is not necessary to do those steps.
just curious did you partition your card? if so what class card do you have? and what size ext partition did you do? if anything go here:http://androidforums.com/evo-4g-all...-rooting-gingerbread-2-3-5-dummies-guide.html and go to the partitioning section for info and instructions. in the "how to install darktremors" section, there is the link that you want. the one that is posted on the unofficial cm9 op is an older version. the one in the guide is the newer version.
no worries. i would recommend that you have at least a class 6 or higher card, if you do not have a higher card already. they will make your apps perform better. most apps can handle just the stock class 4 card. but games and other apps would handle better with a faster card.