So here's the deal. Lincoln was 100% in illegal zone when he suspended habeas corpus. Habeas corpus is a influential and completely needed part of both the American constitution and basic American civil liberties. Basically, at the time of the suspension, Lincoln could have been impeached for violating this. Also, there is no part of the constitution as of 1860 (to the best of my knowledge) that permits the suspension of the constitution in times of war (which technically it wasn't a time of war, because there wasn't a declaration of war). This simply and completely shows that Lincoln was illegal in doing this.
However, Lincoln did have some good reasons to suspends habeas corpus, but this DOES NOT ALLOW for the constitution to be broken. His actions were one hundred percent unjustifiable. While a democracy is the least efficient form of government, it does not allow for the government to simply ignore the foundations of the United States of America.
