While 2-ply yarns is just fine for socks, you may want to consider 3-ply, Navaho ply (3-ply the easy way), or a cabled 4-ply yarn for you socks. 3- and 4-ply cabled yarns appear to make longer-wearing socks, but of course are thicker and can be more work to produce. You must decide for yourself what you want, but you should always ply sock yarn to make it stronger and even out the inevitable variations in thickness we find in handspun yarns.
You should also keep in mind that the amount of twist required in the singles yarn is affected by the amount of twist that will be subtracted when you ply. 2-ply yarn needs more twist, as the tight plying required for sock yarn will subtract twist from the singles; 3-ply requires less twist as there are three strands of singles being twisted in the opposite direction and thus less twist is subtracted from each individual singles. Cabled 4-ply is a yarn that takes some thought and experimentation to come out perfectly balanced—this is one that requires experimentation and note-taking, but is well worth the effort.
Some pros and cons of the different plying techniques:
Advantages: Quickest path to finished sock yarn
Disadvantages: Can wear faster than other techniques
Advantages: Great way to preserve the striping in variegated singles
Quickest way to get 3-ply yarn
Disadvantages: Little bumps can irritate sensitive feet
Requires finer singles and more yardage than a 2-ply of similar thickness
Advantages: Avoids the little bumps of Navaho ply
Allows use of 3 different (in color/texture/content) singles if desired
Disadvantages: Requires 3 bobbins/cops of yarn, all approximately the same yardage
Advantages: The longest-wearing socks
Allows for many effects with any combination of singles being different in color/content/texture
Disadvantages: Takes the longest to spin a finished, with 3 steps involved (4 singles, then two 2-ply, then one 4-ply