E26,
Your panels are amorphous film solar panels. They will not work well with poly or mono crystals as their production voltage is different. There will be other incompatibilities as well.
Your panels need to be the same type and have the same specs. ( A matched pair is obviously best).
For an inverter, you need to think of the startup current pulled for any pump you have or are considering. If your inverter is too small, it won't work. Pure sine wave inverters are much better for anything sensitive.
If you are going to try to get a DC pump and run it straight off the panels, you must learn about Linear Current Boosters or you risk damaging your pump. Yes there are other ways to connect them, but that is even more advanced than using an LCB.
I cannot talk to wether or not your current setup will help or hurt your pond. But I do know you are eventually going to have to decide which way you want to go. Yes you can use what you have, or you can upgrade when you can afford to do so. Either way, learn about balancing your system so you do not damage your batteries, panels, or pump.
If you upgrade one piece at a time, buy the batteries last as they have a "shelf life" if not used and charged regularly.
