Did most men join an army or militia? How did the war affect peoples lifestyles? How did british troops treat citizens of occupied cities? How were loyalist sympathisers treated by the american government?
Did most men join an army or militia?
Over the course of the war, around 250,000 men served in some capacity in the Continental Army, enjoying around 80,000 men at its height. The total population of all 13 colonies hovered somewhere around 2.5-3 million. So assuming the male population was half of that, most men did not join the fighting but a very large portion of them did.
How did the war affect peoples lifestyles?
Depends on where you lived and when you lived there. Boston and Brooklyn were almost completely abandoned in 1776 as the Continental and British Armies vied for control, though the populations eventually returned during the war. New York City also experienced a sharp decline in population and lost hundreds of buildings to fire. Charleston, NC was heavily shelled during the war as well. Slave owners experienced a sharp decline in slave population as many escaped to the freedom promised them by the British. The Episcopalian Church formed when American churches broke away from the Anglican Church. Both sides "foraged", i.e. looted, the countryside for supplies as they marched through. Indian raids also increased sharply during the war as most of the tribes chose a side and attacked frontier settlements. Women picked up the slack at home as their men went off to war, working in the fields or making and gathering supplies and goods for either armies. As time went on, women took a more active role in the war and worked as nurses or took more active roles in the family businesses.
There's a lot more I could say about the subject so feel free to ask for anything more specific if this answer didn't satisfy you.
How were loyalist sympathizers treated by the American government?
Poorly. Thousands of Loyalists lost property to Patriot harassment and fled to Canada to escape persecution. State and national governments offered little in the way of compensation for the financial losses and did little to protect them from mob violence. One Continental Congress resolution ordered the immediate disarming of Loyalists. Patriots seem to have had little sympathy for the plight of the "Tories."
Sources:
John Sibley Butler, "Affirmative Action in the Military," (in Individual Cases), Annals of the American Academy of Political and Social Science
Gordon S. Wood, The Radicalism of the American Revolution
David McCullough, 1776
Dale Anderson, Daily Life During the American Revolution
Rodney Atwood, The Hessians
Alan Taylor, The Civil War of 1812