Welcome to Omniglot! I hope you achieve fluency in all of your goals, especially Arabic.
I see you want to learn Lakhota, that's an interesting choice.
If it's okay, I'd like to add some of my input.
You got phones down, the simple sounds. Phonemes are the smallest piece of a language, single phones, that are distinguishable. Distinct phonemes change the meaning in words which are otherwise the same.
'Sea' /si/ and
'tea' /ti/, are phonetically distinguished solely by the phonemes [s] and [t].
You pretty much got allophones right. An allophone is when two (or more) different phones can stand in for the same phoneme; [p] and [pʰ] are both
allophones of /p/, they are technically the same phoneme. For example, the word
pit, with [p] or [pʰ], is the the same word and has the same meaning.
You were right with morphemes but they can also be words. A morpheme is a unit that actually has any meaning. /s/ (and [z]), like you mentioned, is a morpheme. When added to the end of a noun, it creates the plural. However, words like
cracker are also morphemes. The word
apples is really two morphemes <apple> 'a red fruit'+ <s> 'plural'.