We started with an allotment, then took on a second one. This gave us the space to grow enough to feed a family of four, and the opportunity to hone/develop our growing skills. If there are huge waits for allotments in your area, you may be lucky enough to find a 'garden share scheme', where you agree to cultivate their garden for someone who has a large garden but either doesn't have the time, or because of age or infirmity can no longer manage the work themselves. You then share the produce with them, and undertake to keep the garden tidy.
We were lucky enough to be in the housing market already, so that when, after many years of searching, we finally found this place, we were able to sell up and buy it, then move in straight away. That is buying; we didn't see any smallholdings to rent during our search. There have been a few sad tales here on TAS of private tenants suddenly being required to move out, and struggling to find land to house their animals while they restart their search.
The thing about smallholding is that there's the romantic childhood memory of balmy days on the farm, harvesting veg, playing in the fields and scratching the pigs' ears, but the reality is something else - it's a whole lot of hard work. The idea to try WOOFing or HELPX, where you spend some weekends on other's smallholding helping and learning the realities of smallholding life, is an excellent one. You begin to learn how long it takes to do a job - always longer than you estimate - and how strong and fit you need to be.
I so understand your desire to get started right now, but have a think about the points I've made and see if a compromise couldn't work for you while you get to the point where you could afford to buy your ideal place.