There is a lot to cover here.
First off, I don't think I would trust any powder that I bought from anybody unless they were in unopened containers, even if it were something like Blue Dot that you can see blue dots in. You never know if they mixed something else in there by accident, or if it really is Blue Dot. I know enough about shotshell primers to be able to tell the difference, so I might trust those over the powder.
As a novice, without much experience with the components, you might be better off steering away from old components that might not be what they are designated as. Nothing turns a reloader off to relaoding quicker than blowing up a gun and/or going to the hospital.
If I am not mistaken, the MEC 600 Jr. comes in a 3 1/2" version and you can buy little bases to put underneath the shells to allow it to reload 2 3/4" and 3" shells. However, the MEC 600 Jr. for 2 3/4" & 3" loads cannot be used to load 3 1/2" loads.
As already mentioned, if you are looking at doing non-toxic reloading, you are better off metering out Steel powder on an electronic scale and actually counting out the pellets for each load. Counting the pellets isn't hard once you have a couple empty primer trays. Each tray is 100. If you need 88 pellets, just fill in 12 of the holes with hot glue and then dip the tray into the pellets and pull it out. You might get some stuck in between the pellets seated in the tray, but it sure makes it a lot easier. The reloader is used for depriming, priming, inserting the wad, and crimping the shell closed. The powder and shot are poured in by hand.
If I were in your shoes, I would probably go with a Steelmaster and start with that. Buy some of the shell holders I mentioned to allow yourself to reload 2 3/4" and 3" shells with that press and it is already set up for reloading steel if you really do not want to meter out the powder and count the pellets, yet I believe it can still reload lead shells just the way it is set up.
http://www.precisionreloading.com/mm...ISC_MEC_ACCESS
It also looks like a standard MEC 600 Jr. can be converted to reload 3 1/2" shells. Here is a link, but I have no idea what the conversion kit looks like:
http://www.precisionreloading.com/mm...ISC_MEC_ACCESS