1. So am I correct in saying these two units have the same combat ability?
Yes but this isn't exactly correct, as charge bonus will be the decider, and usually the unit with the higher attack and charge bonus will start getting a cumulative advantage from the moment a contact with the enemy is made (assuming the at+def total is the same).

2. Does shields counts towards def stat of each unit?
If they are designated to count, then yes. As a general rule they do count, unless they got a decimal modifier like 0.5 (eg, CK) or are units which use two handed weapons in melee combat (eg Varangians).

3. Am I going totally crazy or am I going in a right direction?
That I cannot answer heh