If you are going to put to use those garage sale finds the place to start is with a solid working rabbet plane. These will be used more than any other plane in your box. You will use them to do all your rebate and chamfer work unless you plan to use a table saw. One with a straight edge is what you want for work along the grain. Cross gain work usually is handled with a skewed version, thought not a must.
These are not just a wooden shoulder plane. A shoulder plane is expected to take a slicing cut on end grain and usually has a low angle. On the other hand a rabbet plane is designed to rapidly but smoothly cut side grain and thus will have a bed angle like a bench plane. A good rabbet plane will eject shavings out the escapement where as a shoulder plane will quickly clog since it was not designed to cut large amounts of side grain material. A good rabbet plane is a joy to use and a wooden one is light and quick.
To demonstrate I put a couple of videos together to show you how a properly set one will work. First, I I have a left hand side round that I use to set the gage line for my 3/4″ rabbit to track in. I have the rabbet plane set moderately heavy. Watch the shavings really shoot out the escapement as I get going toward the end of the video
Now I show a full width shaving that is set on the lighter side for a 1-1/8″ rabbet plane. A large rabbet plane like this is nice to have. I find I can keep my rebates level and plum much easier and track my gage line by using my fingers as a fence more easily as well.