You don't necessarily need to spend a ton of money getting the biggest cables that will fit into the connectors. The wire sizes that the terminals can accept may or may not match up with the current that the system is able to provide. Just make sure to check what you really need, and get the correct size wire for the job, taking into consideration future needs and possible expansion. Also be mindful that the current rating for a wire is not strictly a function of the wire itself, but also the temperature rating of the insulation on the wire. You can get wire rated for 125 degrees C or higher, which can carry a lot more current without the risk of a fire than the same wire size rated for 70 degrees C. Just because the wire is warm/hot doesn't necesssarily mean that there is a risk of a fire, but you will be running at lower efficiency and may suffer from increased voltage drop. Personally I'd run the largest wire I could because I wouldn't want to have to change it later. But if you have a specific purpose for the system, know you won't be expanding, or have already taken system expansion into consideration, you may be able to get by just fine with a smaller wire and save a few bucks.