Fun fact: "heel" and "whole" are cognates. When you take into account that Dutch uses adjectives as adverbs, you get something like "whole" vs "wholly". And it is easy to see how a word like "wholly" would have its meaning diluted a bit until it starts getting used as a general intensifier - see the word "full", which was used as an adverb meaning "very" in archaic/old timey English, as in "full well".
Progressive tense in English could be expressed in a variety of ways in Dutch. Your way is more appropriate if you want to emphaisize on the continuity of the action. Please try not to make one-to-one mappings with grammatical concepts across different languages; it simply doesn't work. On the 'een heel boek' part, you would place it right after 'ben' - 'ik ben een heel boek aan het lezen'.