Plugsmustard: I'm not sure about your question, but inside you should have a pump sock. That sponge filter won't keep out anything much smaller than boulders. You can get a pump sock from your local hydro store from ten to fifteen dollars or you can carefully stretch and wrap your pump and tower in a short nylon sock that women wear with flat shoes, and they're only about $2 a pair at Walmart. That was a tip I got from Aerogarden's customer service about four years ago and it's golden. Root's had already killed my pump before that.
If you get two plants going you're going to have a lot of roots in your reservoir and it'll be a pain in the ass to take it apart and clean. And that's something you'll have to do every week. You can remove the two spars in the reservoir and it will make it a lot easier to disassemble. The spars are only used by A/G to keep the reservoir's shape during the manufacturing process and shipping. That hint was also from A/G's customer service and it too is golden. You'll want to start an 800 number relationship with them. They'll be very helpful as long as they don't know what you're growing. If they ask, you're growing 'culinary herbs.'
As far as nutrients are concerned, if you have a set of measuring spoons and a pH test kit or a meter, I strongly recommend you don't use A/G's nutes for growing M/J. Go to your local hydro store or go online and try: Technaflora's, "Recipe for Success," sample it. It's a bout $30 and in an A/G it will last you for a long time. Follow the directions to the letter, dump your nutes weekly, scrub your reservoir and you should be a happy camper. HSA
