Let's get down to business.

The first author I'd suggest you familiarize yourself with is Louis Perez Jr. He is one of the foremost scholars of Cuban history (period) and you have the good fortune that he specializes in the late 19th century and early 20th, so his work will give you the before, during and after of the war.

To start learning about Cuba I'd recommend starting with Perez' Cuba: Between Reform and Revolution, which is currently on its fifth edition now. It will give you the broader view of what's happening so you don't feel like you've been dropped into Cuba without knowing which way is up. I definitely recommend this over Hugh Thomas' Cuba Or The Pursuit Of Freedom which is a gigantic text which will flood you with largely useless facts and which owes almost everything interesting it says to other authors who Thomas has gleaned from in order to produce the book.

Once you have that under your belt, read Cuba Between Empires, 1878-1902, which goes from the beginning of the peace which followed the first independence war to the end of the American occupation and thus the beginning of the Cuban Republic.

Now, with a good understanding of WHAT happened, you read The War of 1898: The United States and Cuba in History and Historiography which is going to explain how people have WRITTEN about what happened. Basically, how narratives have been built around the war, what purposes they served, and how specific narratives are flawed. You can also mine the bibliography that this book cites, along with using Perez' summaries of what their books basically say, to get into the nitty gritty of issues from the war that interest you.

Now, primary sources. The big figures from the war are: Jose Marti, Antonio Maceo, Calixto Garcia, and Maximo Gomez (he's actualy Dominican by birth but let the armies in both independence wars).

Marti is a warrior-poet who had a great historical film made about him called Jose Marti: Ojo del Canario which you can find online, in full, with English subtitles here: https://www.youtube.com/watch?v=ff8amV9VWCo

You'll want to read, if you want to really get into primary sources, the diaries of Maximo Gomez. He kept notes throughout the war and as I recall his reaction to American intervention was... Interesting.

Antonio Maceo died before the US invaded but was also extremely wary of support from Washington, as you'll see in the already cited sources. He is shot during a raid into Spanish held territory and Maximo Gomez' son tries to carry his body away in the middle of the skirmish. Gomez' son is hacked to bits by machete blows from Spanish troops. Gomez never really got over that (he should have been captured, not slaughtered).

The most interesting source I can think to cite on this period once you get into really specific details is Herminio Portell Vila's classic Historia de Cuba en sus Relaciones con los Estados Unidos y España but... That had one edition, it was over 80 years ago, and it´s only in Spanish. The book itself (in several volumes) is exceedingly rare, but you´re welcome to try to find and read it.

Hope it helps!