Good stuff man! But yeah, if you're going to do any further development, I would 100% recommend not using any more league assets (lol)
On that note, I really like your idea of upcoming characters! There are plenty of "open source" characters that you can use, many of which are already in LoL, such as Wukong. So, you could have a character called Wukong, who is a monkey with a staff that can change size etc, but probably best not to use the same skills exactly as they are. You could read more into his lore and come up with your own stuff...
Some LoL stuff is loosely based off of other stuff which has then be adapted enough to not cause copyright issues; for example, Khazix is "Alien", and Rengar is Predator, and their sub-quest reflects this
For more characters, you could look to other areas of mythology, such as the Greek and Roman gods, Asian gods, Egyptian gods, African gods, etc etc etc
Sorry to babble on so much but I really love the idea of developing a moba from scratch, and the option for online play would definitely be a good idea. Photon plugin would be perfect for this!
Good luck with your project! There is no reason why it cannot be successful and you cannot make good money from this