It's really up to you - is it your main source of heating or is it more to make the room feel cosy? You certainly don't need a roaring fire to get heat. Once it's been burning a while, an occassional top up will keep it going, as the embers give off some heat. Remember it will continue to give off heat for a while so don't have it burning full blast just before bedtime for example. You should be able to light it with some old loosely scrunched up newspaper and dry twigs, rather than bothering with firelighters. You will need something to 'poke' the fire with, rearrange logs etc. Companio sets can often be found in DIY shops, antique shops and specialist fireplace shops (yes they do exist)
Yes - you can't go straight to big logs, give it a chance to catch first. The twigs/sticks really need to be completely dry. It's worth ahving a stash in a shed, log basket if you are really going to be using it. Ours gets used at Christmas - well until we had the kids anyway. It is quite handy ina power cut though!