I’ve only made cider a couple of times, but we do brew beer regularly, and some of the questions are common to both.
The main dangers to the “shelf life” are secondary fermentation and stray yeasts and moulds that will spoil the drink and turn it to vinegar (or worse). I take it that you’re not too worried about a bit of oxidation or a bit of cloudiness.
If you’ve bottled the cider in sterile plastic bottles they should keep for several weeks. Beware of any signs that fermentation is restarting, since the bottles won’t be strong enough to contain much pressure.
Personally, I’d rack the big containers again rather than leave the cider lying on a layer of dead yeast, which will eventually give it an off-flavour.
I’ve experimented with the plastic barrels with a CO2 bulb. Really, they’re intended to keep the headroom full of CO2 as a naturally sparkling drink is dispensed. They work well for the livelier beers, but since cider is usually not very gassy you’ll find it a very expensive exercise to keep replacing the little bulbs as the level in the barrel drops. The other problem is that unless you’ve got a dedicated fridge, you can’t keep the barrel cold. If you prefer your cider chilled, I think that it’s better to use bottles. I have to say that although we still use our plastic barrels, they’re used for bitters and brown ales that are drunk at room temperature, and I gave up the Sparklets bulbs and went back to a plain lid.