That's how I started studying Japanese, by learning hiragana & katana as a prerequisite... I'm pretty rusty w/ katakana now because I'm out of practice--- I'm not overly fond of katakana.
It's good though to go about learning kanji through a regular coursebook rather than just sitting down and memorizing a bunch of characters. Course books like
Minna no Nihongo,
Japanese for Everyone, &
Genki start with hiragana and gradually ramp up to kanji usage, which is then reinforced with each lesson... I think it's better to study Japanese as a whole process than each thing discreetly, though reference books on grammer, kanji, particles, verbs, adverbs, etcetera always help. Just don't go out and buy a bunch of books, start with one course book and add books as your Japanese level dictates...
Your best bet for books written entirely in hiragana are books written for children which you should be able to buy off of amazon.co.jp, also, you might be able to order them from
Bookoff, a large used book chain in Japan, but I'm uncertain about shipping.
Good luck.