The constitution states
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
This means that the President is president until the moment that the Senate convicts, and is not President thereafter. Until the moment of conviction they have all the usual powers of President, and after they have none.
Details like "where does the convicted President sleep" would be dealt with on a case by case basis. It would be within the powers of the incoming President to authorise the impeached president to spend the night at the White House, until their affairs were in order.
The "nuclear football" goes with the President, but the VP has their own "football" (in case the President is incapacitated in a nuclear attack). The contents of the briefcases containing the nuclear codes would be sorted out in the following days and when a new VP was appointed., but at no time would America not have the ability to fire her weapons.
The impeached President doesn't get to issue pardons after he has been convicted. The incoming President can issue pardons, and can pardon the impeached President for any criminal charges (as Ford pardoned Nixon after the latter's resignation)
The handover of power would be fairly straightforward. Certainly it would a lot clearer than if a President dies in office. After the Kennedy assassination and after the Reagan shooting there were periods of confusion. These were unexpected. During an impeachment trial, the likelihood of conviction could be known in advance.
If a President were impeached and there was a likelyhood of conviction, much of their influence would be lost, and there would be a period during which all their time would be spent on fighting impeachment. They wouldn't be able to advance their policies in Congress (especially against a congress that had voted to remove them from power) They would have all the constitutional rights of President (including the granting of pardons) but little of the influence or soft-power.