I would recommend scanning at the maximum possible resolution and near to the size of the originals. Store them as lossless jpg or another lossless format in case you want to change them.
There are a number of organisational systems. Why not try arranging them chronologically and titling them and keywording them by themes. You might also want to put dates into the title.
If you want easy retrieval you need a filing system based on a restricted vocabulary. To some extent you have to make your own (Family, friends, holidays, motorbikes..... whatever) and then have the discipline to use it.