I'm not sure what the process is - other than I just sit down and start to write the thing. But the pattern is pretty easy to describe. In every battle (actually in every book, but we'll leave that aside) there's a big story and a little story. The big story is the description of the real event - so at Waterloo it's the tale of the British retreat to Mont St Jean, the decision to stand there, and then the various French attacks on Wellington's position. The little story is Sharpe's role in all of that, and right from the start there are one or two events which I know I want him to be involved with - thus the closing of Hougomont's gate and, especially, the wounding of the Prince of Orange. The perverse aspect of this is that the little story is mostly in the foreground, while the big story is in the background - that, I suppose, is what makes a fictional account of a battle very different. So I suppose that when I research a battle I look for those small events where Sharpe can make a difference, and draw the plot back from them - so in Sharpe's Waterloo he's always getting ticked off with the Prince of Orange, because that makes sense of the attempted murder.
I'm sure the best fiction has a tight unity of time! But others, of course, disagree. I find it almost impossible to write multi-generational sagas ('and so the age of dinosaurs passed imperceptibly into the information age'), but others like to write them, and they do very well . . . so I guess you pays your money and take your choice! Theatrical? Maybe. I'm an avid theatre-goer, so perhaps that's an influence. I hate flashback. I cannot describe how much I detest flashback. On occasions it's unavoidable. I was given a book the other day and found that it was almost all flashback, so I simply junked it. But that's me . . again, other people like it! Essentially, though, time flows forward and that's how I like my fiction.
Wow! I'm going to guess that you mean what historical fiction should a young writer read? If it's non-fiction then, of course, it entirely depends on what period you want to write about - but if it's fiction technique that you're after then the best advice (which sounds, alas, unhelpful) is that you read everything by the authors you like - because those are the authors whom you're going to emulate. I'd certainly get hold of some George Shipway and C.S. Forester, and Alexander Kent and Dudley Pope. What you do with those books is note what you like and what you don't like, so that you can leave out the things you don't like and put in more of those that you do.
For my sins I must confess I've read neither . . . sorry.
That the prospect of facing 130,000 words is not in the least bit daunting . . . it seems insuperable when you start writing, but after a handful of books it isn't daunting at all. Hope this helps!