you can do it just fine with a portable a/c. couple things first off.
you shouldn't be pushing air through your carbon filter. the air will not be going over the prefilter first and will shorten the life of the carbon on your filter.
the problem with most portable a/c units is that they are single chamber which means that the air in the room and the air used to cool the unit are mixing. they sell high end units that are dual chamber but probably way more than you want to spend. in your case i would still get the portable ac but i would connect the exhaust hose to a inline carbon filter. don't suck air from the ac using a fan or anything...this will burn out the motor on the ac. just filter the air exhaust before sending it to the attic. a cheap way to do this would be to just build your own filter box for the attic and axhaust your ac into that. you can buy sheets of hepa and carbon filter at home depot.
water cooling is amazing but probably more than you want to spend. i use ice boxes, water cooled air handlers, big and small chillers and absolutely love them. i will never go back. they are 40-50% more efficient than ac's and allow you to cool more equipment specifically like co2 generators and reservoirs. the drawback is that it's probably double to triple the price of a standard ac setup to cool the same space. you make that money back quickly on your electricity bill but most people don't want to throw down that much money off the bat. the other thing is that water cooling is not really an option for anything less than 2,000w cause the chillers that you want are not the cheap ecoplus and active aqua ones. you need commercial hillers like chillking. this is where most people messup. they get a 1/2hp ecoplus chiller and the wrong soze reservoir and expect a single ice box to cool their light and their room. doesn't work like that.
anyway, i'm rambling...
you'll be fine with the portable ac. just filter the exhaust somehow. for your lights...if you are pulling air from outside of the room then you don't need to filter the exhaust. if you are pulling air from inside of the room then switch the fan and filter. put the filter on the intake of your lights and pull air from the room, through the filter, through the lights, and exhaust it into the attic. if you get the ac then i you will need to make the air going through your lights a closed loop somehow.
edit: agree 100% with super. adding co2 is not the answer to high temp issues. it will only lead to more problems.