Appropriate conduit for several data cables underground over 300' run
Speaking as someone who does a LOT of data cables...

Pray to your deity of choice regarding (lack of) lightning nearby. The extent to which I prefer fiber optic for outside data runs is influenced by years of dealing with copper outside data runs, and the failures resulting - but few, if any, cameras are set up for power + fiber optic, so you'll want a nice POE-friendly surge suppressor at the point where these cables enter your building, tied into the building grounding/earthing system. Else you will have burnt out data ports, almost certainly, eventually.

As already mentioned, don't even think of putting non-wet-rated cable in exterior conduit. It may work for a while, but it will fail, usually at "not a good time." I personally prefer a "dry gel" cable and tend to get stuff which purports to be direct burial, but I run it in conduit as I hate digging trenches twice, and I trust rodents to chew on direct burial cables.

You can not bother to glue the joints at all, or you can glue the joints with great care. If the conduit is PERFECTLY waterproof, it will still fill with water, as moist air will enter and moisture will condense, and stay in the conduit. All outside conduits are defined as wet locations, and all cables in them must be wet rated, or failures will be expected. 

Run 2" conduit if you like, but it's going to be massive overkill for four 4-pair data cables unless you get some absurdly thick jackets. Nice to have more room than you need, but there is a point of absurdity. Two examples of 24AWG Cat 5e direct burial in stock are right around 0.25" diameter for a net area of 0.05 square inches each - roughly equivalent to 6AWG wire, where (less than) 40% fill would be 1" (rigid) schedule 80 conduit, (or 3/4" schedule 40, but I prefer 80 by a large margin.) So 1-1/4" would be more than generous sizing and cost you quite a bit less. Where things are more unknown, 2" is nice just because if you don't know, you don't, but if 4 data cables is it, 2" is, IMHO, Massive Overkill. Save your money for something you actually need... Like those POE surge suppressors (not cheap, but inexpensive as compared to the equipment you will lose otherwise.)

Most "real" POE devices work just fine at 100 meters on 24Ga cable from the 48V POE power supply - the device power supply is generally flexible and expects to be able to work on a short cable at full voltage or a long cable at lower delivered voltage, and most are not power hogs anyway. Early "half-baked" POE systems varied a lot more wildly, as may things which ARE powerhogs and outside the "real" POE standards.