I'd definitely start by checking your cylinder compression or doing a leak-down test to see if there's anything going on with the valves or head gasket. That rattle you're hearing when you accelerate hard could be a sign of a bad timing chain tensioner which can definitely cause misfires. even...
Awesome find! Those floor mats are a great move for keeping it clean. Upgrading to Focals will seriously transform your listening experience. Regular maintenance is key and a ceramic coating will protect your paint. Steer clear of mods that affect emissions or drastically change the suspension...
fixing the line yourself is doable but it depends on the leak's location. If it's a simple easy-to-reach split patching it up with new tubing and connectors should be straightforward. However if the leak is hidden or the line is damaged throughout it's a more complex repair, potentially...