Hey Luke, well no you don't need an amp. They will run off that headunit. However it might not be very loud. The h/u puts out 50W/channel max. Which is probably more like 20W RMS (couldn't find an RMS figure). (For basic understanding, just look at RMS figures). People with more knowledge than me can tell you about the other power figures, sensitivity etc, but for basics for non-audiophiles that's the main thing you're looking at here. All those other figures might tell said audiophile roughly how loud it will be, but not me.
So if you want to amp the system, you will be looking for a 4 channel amp. Those speakers are rated at 110W RMS and 100W RMS, so you're not going to want anything putting out more than about 100W RMS per channel @ 4ohm at 14.4V. Any more is pointless unless you planned on upgrading the speakers later on. And you probably don't need that much power either.
I'm running Alpine SPX-17REF (75W RMS) and an old Alpine V12 amp that puts out 80W RMS. (I run a 12" sub off the other 2 channels, being 150W RMS though the amp puts out 200W RMS bridged). So I wouldn't use it at full volume, that's a more powerful amp than I would ever use with these speakers. ie- waste. Hope that all helps a bit.