Why does Dracula want to move to England? What do you make of his collection of English books, maps, etc., and his desire to speak like an English gentleman? Why might Dracula’s move to England and his collection of English texts be viewed as preparations for war to Victorian readers?

Dracula wants to move to England because it was, at the time, the center of the world's most powerful empire. Britain was the most admired and feared superpower in the world, and its culture was envied and emulated. For someone as ambitious as Count Dracula, it would be the natural place to move. It would also be natural for someone with his large ego to want to be that most admired of figures, a learned and cultured English gentleman. Further, ships went all over the world to and from England's ports, which would help him with his plans for spreading vampirism.
Victorian readers might have perceived Dracula's move to England as preparation for war for two reasons. First, we as readers are explicitly told through Harker's and Seward's journals that Dracula is coming to England to create an army of vampires and wage war. From Harker's journal we read the following:

This was the being I was helping to transfer to London, where, perhaps, for centuries to come he might, amongst its  teeming millions, satiate his lust for blood, and create a new and ever-widening circle of semi-demons to batten on the helpless. 

We further learn from Dr. Seward's diary: 

So he [Dracula] came to London to invade a new land. He was beaten, and when all hope of success was lost, and his existence in danger, he fled back over the sea to his home; just as formerly he had fled back over the Danube from Turkey Land.

This idea of vampires from an exotic land invading played on people's fear at the time of the seemingly strange, unnatural foreigner invading. Britain was at the height of empire at this period but also increasingly beginning to worry about being headed for decline. Also, like France and the United States, England feared being swamped by non-Nordic immigrants. For example, as Latour argues persuasively in his The Pasteurization of France, France took Lister's ideas of bacteria seriously because the country was worried that white French people would be wiped out by the periodic disease epidemics that hit and the nation then swamped by darker-skinned foreigners. And a quick glance at the racist Tom Buchanan's sentiments in The Great Gatsby shows that fears of the non-Nordic foreigner invading were still prevalent in the 1920s. In Dracula, we see the same anxieties in English culture. Count Dracula is fought by doctors as a disease.
These fears of pollution and invasion morphed into fears of sexual union with the foreigner. As we know from Dracula, the bite of the vampire, with its sexual implications, is what pollutes the blood of pure English women and turns them into something alien and fearful. 
The average Slovaks who live near Dracula's castle are described as exotic. Harker writes:

The strangest figures we saw were the Slovaks, who were more barbarian than the rest, with their big cow-boy hats, great baggy dirty-white trousers, white linen shirts, and enormous heavy leather belts, nearly a foot wide, all studded over with brass nails. They wore high boots, with their trousers tucked into them, and had long black hair and heavy black moustaches. They are very picturesque, but do not look prepossessing. On the stage they would be set down at once as some old Oriental band of brigands. They are, however, I am told, very harmless and rather wanting in natural self-assertion.

Even such "harmless" people, because they are different, can hide a malevolent invader like Dracula. It is easy to see, therefore, how Dracula's move to England would play on Victorian anxieties.