Short Overview of the Four Alphabets of Japanese

Romaji

Basically just the English alphabet.

Has no particular purpose.

There's really no need to learn it, as I've been told on numerous occasions from various sources.

But there's essentially nothing to "learn" about it, it's literally just the English alphabet, but with Japanese pronunciation. And if you were for some reason, to choose to learn Romaji instead of Hiragana and the other alphabets, you could actually risk messing up the pronunciation of the words because knowing the alphabet, there are loads of irregularities, making it a little bit difficult to learn Japanese that way.

Hiragana

Probably the most used alphabet, unless Kanji would be more used, I'm not quite sure.

Definitely the first alphabet to learn.

Hiragana, from what I can see, is similar to Katakana, excluding the fact that the sounds are the same.

More curvy-looking than Katakana.

Katakana

Has the same sounds as Hiragana.

Is more box-shaped.

Has shapes that are similar to Hiragana.

Kanji

These came from China.

For the number of Kanji to learn, it would probably be around 2000, and something like 2500-3000 if you are/were a student.

Probably the hardest alphabet to learn.