2nd How did the Do-217 compare to similar (that is contemporary two-engined) bombers of other nations?
By the time the Do 217 makes its appearance in service the principal Allied countries are introducing four engined heavy bombers, which, in terms of bomb load and range, and performance in some cases the Do 217 simply cannot compete with. Nevertheless, it was an impressive aeroplane and as Tomo pointed out it can be compared with the Manchester, but only broadly, as the Manchester was bigger and heavier than the Dornier and could carry a larger load, but performance wise, the Dornier demonstrated better speeds and combat radius with smaller loads.
Compared with another Allied twin engined bomber of similar vintage, say, like the B-25, the differences are less pronounced in terms of size, weights, engine power output, but again, the Dornier has a greater load carrying capacity and is faster with a longer range, but the B-25 is not a heavy bomber and it is better defended with power turrets and has a larger crew. The use of these two aircraft by their respective air forces was quite different, so it is more difficult to draw a meaningful comparison between them.
The employment of the twin engined long range heavy bomber was borne out of necessity and Luftwaffe doctrine - there's a thread about it elsewhere here and as we know the plan was to introduce the He 177 and the result of the Bomber B spec from 1941 onwards, but this all went sideways for various reasons and the Do 217 became the more reliable of Germany's heavy bomber force, since the He 177 was a basket case and took waaay longer than it should have taken to get into service in numbers. The Do 217 was unique - it was a twin engined heavy bomber with a big warload and credible performance and certainly had better reliability than its Heinkel offsider, but would it have gained prominence if the He 177 was more reliable and entered service as was originally intended?