Yes I'd put a normal plastic pot inside, the same diameter as the external container (or as near as poss) but not necessarily as deep as the buckets. Many container plants don't have very deep roots so by doing that you wouldn't need to fill the whole bucket with compost, which would be heavy and a waste of compost. I reckon about 2/3rds the length of those buckets in the picture?
For this time of year, you could try pansies, violas, cyclamen for flowers; you're also not too late to plant tulip bulbs for flowers next spring. Hanging baskets and containers in general look better with some foliage plants to give them some structure, eg ivy to trail over the edges, or ferns or heathers in the centre to give height. Have a look on Pinterest for winter container planting, there are loads of lovely ideas. A decent garden centre should have a variety of plants suitable for planting now, but you can get a tray of pansies in Sainsbury's 
Container gardening can be more labour intensive than planting in flower beds, even in winter they can dry out if they are in the rain shadow of the house so just keep an eye on how wet they are. You want moist but not waterlogged.
And don't worry about being a novice! Part of the joy of gardening is learning as you go along, finding out what works in your garden and experimenting with different plants. None of the plants I've mentioned above are very expensive, so it's worth a try.