Thank you Jan. Just so!
Another that perhaps could do with being added are the common 4 species of courgette, pumpkin and winter squash. Most people grow them, all allotment situations grow many of them and to isolate and handpollinate is a must for 3 of the 4 species. The fig leaf gourd aka shark fin melon is the exception as there is only the one variety in common circulation. But for the others, it is advised to be careful. The green courgette, the acorn squash and the orange halloween pumpkin are in the same species for example, they are all cucurbita pepo and will cross freely. A couple of years ago there was the bitter issue too with cucurbita pepo. Because some ornamental squashes are bitter and can make you ill if you eat their fruit, people who just 'let courgettes cross' can get bitter courgette plants accidentally. Even a commercial seed company accidentally sold contaminated seeds with the bitter gene.
Unfortunately seed companies are usually very bad at adding the species information for cucurbita, so if in doubt, assume they can cross with something else you or others are growing in the vicinity. The crossing is done by bees and other insects including flea beetles who love the yellow flowers, so special measures are needed to produce pure seeds, and bees can fly for a mile easily to find food.
Many crops only produce seed in their second year, so winter storage is something that comes into seed saving. It also means that you have crops growing for much longer than you do for growing to eat, so you need a bit of extra space available.
And the extra space needed includes tolerant spouses and families, because invariably we take up extra space indoors to dry these seeds down to avoid mouldy masses. Not every family will tolerate the drying space needed. And this includes the disasters that pets and children can do to drying seeds. One of our seed circle participants a few years ago told us about their very tidy parent who removed and binned all that messy 'debris' left on a windowsill.
But it is all do-able. And as Jan said, you can start with easy, but just as interesting crops.