Recently, I've been reading through A Course In Mathematical Logic by John Bell and Moshé Machover. However, it's not always the easiest book to understand. What might be some good supplements to have on hand while continuing this read? Alternate book recommendations are welcome, but I'd ask that such recommendations have topical coverage which is comparable to Bell and Machover. That being said, references to lecture notes or courses taught by individuals who used the book are preferred.
Moreover, I was wondering if anyone is aware of published (or unofficial) errata for the book and whether or not an answer key exists for select exercises so that I may check my understanding for more difficult problems.
I'd recommend Goldrei's 'Propositional and Predicate Calculus', Boolos / Burgess / Jeffrey's 'Computability and Logic' and Hedman's 'A First Course in Logic'.
The first is a very clear exposition of first-order logic up to basic consequences of compactness and the Löwenheim-Skolem theorems. The second is a classic exposition of recursion theory and Gödel's first incompleteness theorem and contains surprisingly accessible proofs of important model theoretic theorems, like the interpolation theorems. The third is a wide ranging textbook on model theory, proof theory and recursion theory and contains lengthy chapters on basic model theory, even touching on simple theories.
As a sidenote it may be worthwile to have a look at Machover's 'Set Theory, Logic and their Limitations', which has some topical overlap with the textbook he coauthored.