As a forweord, I would just point to the fact that Medieval Latin is a house of many mansions. That applies to style, respect of Classical Latin grammar rules as well as content. Keeping that in mind, I'd say that grammatical differences are numerous but do not impede reading that much. The biggest hurdle in my view would rather be the totally different cultural mindset and pertaining vocabulary. But even this isn't that much of a problem as long as you're ready to struggle a bit in the beginning.
My advice would be to get some ML reader, they usually include a grammatical summary, various texts and a glossary. I particularly like Reading Medieval Latin by Sidgwell (lots of notes and introductions to the texts) and Beeson's Primer of Medieval Latin (less numerous notes and shorter introductions but a greater number of texts).
Recommanding any work is difficult because this would highly depend on the kind of texts you want/like to read. Here is a very, very short list of some works I like :
- Bede's Historia ecclesiastica gentis Anglorum
- Abelard's letters
- Hroswitha's plays
- Geoffrey of Monmouth's Vita Merlini
- Carmina Burana
- Alexander's romance