You can get Professors Idel's books on him, but nothing quite compares to the impact and shock of actually reading his own words and visions.
It might seem I am not in favor of mystics, but that is only partially true. I am against kabalists and mystics from the dark side as all of them are today. But a true tzadik like Rav Abulafia I have only the greatest respect for.
[The Chida writes very positively about him and adds "The Rashba (a Mediaeval Torah scholar) treated him as a common and empty person, and I do not know why? He was clearly a great man.]
The thing you have to know when it comes to mystic things is you need to get it from the realm of holiness. The trouble with the cult the Gra put into excommunication was they are from the Devil and therefore can not be trusted even when they say seemingly right things, and do what seem to be kosher deeds on the surface.
[Just for public information I ought to mention the aspects of mystic tradition I think are OK: Sefer Yetzira, Rav Abulafia, the Ari (Isaac Luria), the Gra, Rav Yaakov Abuchatzeira and his current day descendants, and the Reshash (Shalom Sharabi)), the Remak. ] Outside of these one must run from what disguises itself as Jewish mysticism but is actually from the Satan as almost all modern day kabalists are. Not to mention the cult the Gra put into excommunication because he saw they are from Satan, though they try to cover up their unkosher, unholy inner essence with Jewish rituals. You need to burn whatever they touch.
I am not saying I understood the Reshash. But I think he is very important in order to understand the Arizal (האריז''ל), but I just never got that far with him. It was mainly the Intentions of Sukka (כוונת סוכה) and Drush HaDaat (דרוש הדעת) that I did fairly thoroughly in the Rehash. And that actually went along well with the Intentions of the Omer (כוונת הועמר) that I did in Shar Hakavanot and also in the Sidur HaReshash (סידור הרש''ש) by the grandson of the Reshash.
I should warn people that I do not think anyone should look at even this very important stuff until having finished Shas with Rashi Tosphot. --a warning offered by the Ari himself in at least two places with surprising severity. [My personal favorites are the עץ חיים of the Ari and almost anything the Remak wrote. Rav Abulafia was not my favorite reading, but I copied down some of his major unifications and used to concentrate on them a lot as he said to do. I think I would have to say he is my favorite mystic, and my second would be the Ari.]
[Some of the obvious problems are that people get mixed up with the idea that the mental "high " they get from this is somehow connected with Devekut [soul attachment with God]. But there are a host of other problems.] There are mystics that get attachment with God. But that is rare and it is not the kind of emotional high that people think.