No internal amp isnt a big deal. What speakers are you gunna power with a HU amp anyways? Hopefully not your front stage, maybe rear fill or a set of tweeters...
That number is probably peak watts or max power which is a useless number. You want to look at the RMS output info. I think your definitely ok with 4 gauge and the whole CEA ratings are still a joke considering the process the follow to get that number. Using test tones isn't very effective to...