Suffice to say I cannot teach you how to sand a floor by email. And I doubt that the rental places will give you a course on sanding and finishing your floor. The "toy " floor sanders they rent at all the tool rental shops will not, in any case, do a decent job of sanding your floor.
But before you consider sanding, read the second part of the floor maintenance article available in the search box at the top of this web page, there are many alternatives. Also read the chemical stripping article in the same section.
I strongly advise you hire out the sanding part of the job. Nobody I know that has sanded their own floors will ever do it again. In most cases they have used far too much time and sandpaper. Then the results were from barely passable in low light, to downright butt ugly floors. The problem with DYI floor sanding is one, the machines, they are light duty, and will leave pronounced chatter marks in your floor. And two, the machine operator, who has little or no training to pass this machine smoothly and evenly across the floor. Most of the mistakes are made in the first passes with coarse grit sandpaper, and these cannot be removed with the fine paper. The amateur does not recognize thing are going wrong until the finish is applied, but by then it's too late.
Pine is very soft, and unforgiving so one slip and your old floor may be gouged forever. Even a lot of pros have problems sanding and finishing this wood. Best to have it professionally sanded, and then consider doing the 4 coats of oil modified polyurethane yourself. Be sure to read my article available in the search box at the top of this web page, on how to hire contractors. When viewing a contractors past work, be sure to see his pine floor jobs.
And if you need advise on brushing the 4 coats of poly, I'd be glad to help you further. Just ask. If you wan to see a good video on floor sanding, please looks at the reviews available in the search box at the top of this web page.