Tim Strazz is a reputable name in the Android hacking world, along with JCase (aka justincase)
Whoever told you Android malware is not very big, they are retarded. Think of how many android root methods there are for various devices. There is a broad range of various android root exploits. These when used in a manner that is malicious is defiantly malware. Take for example geofags towelroot. This is a root exploit for several compatible devices that doesn't even require a reboot. Although this is a great tool for people who WANT to root their phones, this is actually a really nice malicious payload. Embed this in an app to silently gain root and a lot of possibilities exist.
As far as what to learn Java is a great start. However you will also want to have C/C++ as well as ASM. Also get familiar with Linux, as well as SELinux as well as android and the android kernal from various manufacturers. Decompile and reverse engineer apks and decrypt obfuscated code. All this will help you with learning how things work, how to change them and ultimately help in identifying malicious code.
But for now start with C/C++ (androids native language, low level) and Java (high level) as well as ASM. Various exploitation techniques, shellcode, buffer overflows, etc. There is a lot to learn + constant changes
Good luck and I hope you contribute what you learn and your progress in your endevour
