Shout out to all the widows on Mumsnet- there's quite a lot of us!
I will not be commenting on the 'too soon' or whether he's the right guy or any of that stuff. That's all very personal to you and fine by me.
I would have a think, though, about how you want to approach this with the kids. I think you need to start up some conversations, both with the older and the younger ones (sounds like you have an age spread) about all kinds of things- their dad (which it sounds like you do brilliantly), dating and meeting someone else, what life might look like if you did that, how they would feel, what types of things they are concerned about- and that takes time.
I wouldn't rush to have him over for tea, let's just put it that way. You might find a couple of kids are fine with it, one might not be. They might need counselling or more conversations to work out how they would feel. They might think they would be fine with your new guy and then feel really angry when he actually turns up. Somewhere for them to talk, preferably not you (e.g. counsellor, teacher, auntie perhaps?) and then talk with you is what's needed here.
Presumably they know you are in a relationship if you don't have anyone else caring for them?
So this is more about starting conversations than acting. I wouldn't worry yet about what your actions are going to be til the conversations are up and running.
I know my teens are delighted I'm dating again, happy if I meet someone- but would really not like anyone to move in, for example. Our home is our 'safe space' during what has been a horrendous few years and no-one wants to rock that boat. That's fine with me as I don't want to live with a man right now anyway!