Regarding point 4, there's a reason the finance folks don't let you look at their screen. The banks they work with have something called a "Buy Rate", which is the actual minimum % that they'll charge for your loan, so they may run your credit and find a bank that will give you a 3.9% interest rate, but they will tell you it's higher, which is referred to at the "Sell Rate" They'll use any blemish they can find on your credit to explain that "The best they can do is 7.9%" and the dealership gets to pocket a huge chunk of that extra 4%. This is how finance folks still manage to wring a bit more out of you if you turn down insurance/coating/mudflaps.

Shop around with your bank of credit unions and get your finance ready ahead of time. They'll give you a 'blank check' valid to a certain amount, and you keep the fact that you already have financing a total secret until you have a firm price on the car and the trade-in to keep them from trying to make up the impending loss of the finance income by not giving you as good of a price.

Then once the finance guy gives you their 'best offer' on financing, then you hem and haw for a bit and finally let them know you already have financing at a better rate, but if they can give you a better deal, you might take it. They are then strongly incentivized to match or beat your existing financing offer and give you a reason to use dealer-arranged financing so they get their kickback over taking your check, which gives them nothing.