If I have one that is say 4 litres, can I use less ingredients if I am only cooking for 2? And would you go for one with a set time timer ( digital and much more expensive) or is that really not necessary ?
I wouldn't go for the more expensive model. I have a fairly basic model and I'm quite happy with it. Not sure about using fewer ingredients as I fill it and freeze the excess for another meal.
I always recommend a visit to "The Works" (cheapo bookshop)....they have a good selection of slow-cooker books which have not only recipes but also lots of hints/tips to get the best from them...for example, using much less liquid at the start of the cooking.
You just put in as much food as you need to cook. Remember you dont need lots of liquid, it doesnt reduce in the slow cooker. Mine is a basic model with no timer. I just leave it on whilst at work and when i get home i switch it to warm.
I've only got a tiny, 1.5 liter one now. It's enough for two good portions, depending on what is being made. A 3.5 - 4.5 ltr model will be adequate to do a meal plus seconds/leftovers.
My little one is from Wilko, and has lasted ages.
For trying out slow cookers for first time, I'd just go with cheap one, see how often you use it before investing in the digital, expensive model, my two are cheap, they do the job and I love them for handiness, as I said on last thread, great for batch cooking and if I want to go back for seconds. A good suggestion there to you was get a plug timer, they are great