Larry,
Welcome to the forum.
On the draining...should be no need to rent a pump. Use the vacuum hose in the skimmer. Should let you drain well below skimmer level. Or, you can get a cheap Flotec sump type pump at Home Depot for $70 or so. Handy thing to have anyhow.
But...consider this....since you are looking for a major water change, some people have used a big plastic sheet to cover the pool as a separation membrane. If the width of the sheeting isn't enough you can tape sheets together using multiple layers of duct tape. Doesn't hold up long but will be good enough for the couple days it needs to hold. Cover the pool and start adding new water onto the top while you're draining out the bottom. 100% replacement. You never get a 100% replacement if the liquids mix. Another advantage is the water level never drops so you don't have to worry about floating the pool or liner. It does work. Saw a local with a new pool installation doing this last year.
Al