FleurdeLeeds
There are 2 years and 3 months between my 2 boys. The biggest shock when having DS2 was finding out that he was NOTHING LIKE DS1 in terms of his nature. DS1 was fairly demanding as a baby in that he had colic, but dS2 had it MUCH worse. DS1 is laid back and has always been well-behaved. DS2 is as far from laid-back as you can imagine. He has been a nightmare, demanding child from day 1. BUT he is a lot less "serious" than my first -when he's in a good mood he lights up the room and makes everyone laugh, and is so lovey-dovey cuddly (something which DS1 never really was, and still isn't, at age 4 and a half).
What I'm trying to say is that how hard you will find it depends largely upon each child's personality. Yes, DS2 was demanding, but it meant that my laid-backish 2 year old toddler was very patient with a screaming newborn and didn't get too jealous. I was at soft play the other week and she clearly experienced it the other way round. Young baby was being brilliant, 2 year old brother was a screaming, whinging nightmare. My sister had the same type of thing - really difficult son first, then charming, easygoing daughter. There's no knowing what you'll get till they come out!
I don't know anything about your first child's personality but that may come into how you cope with the stress of a second. Not that it should be a factor in whether you decide to go ahead or not - we all got over a horrid first 18 months when DS2 was born (DH away a lot and needed a LOT of support from my parents during colicky evenings - do you have that support?) Now my heart melts when I watch them play together, they love each other to bits, and now that my first has started school, DS2 is missing him and can't wait to pick him up each afternoon!
Other posters have pointed out that your first child can go to preschool soon (if not already) so you will have plenty of time to spend with a second baby, and de-stress a bit from the hassles of having 2.
I found that the worst thing with having a second (apart from the obvious like NEVER, and I literally mean NEVER, having any time to yourself for a couple of years), was that I missed my lovely trips out with just DS1. He was at a lovely age for going to the playground and toddler groups etc, and then all of a sudden I was very restricted with what I could do with him, as DS2 was so bloody demanding and cried a lot and I really had to/wanted to avoid going to public places as he was that stressful!
Having said all that, I would not change things for the world, and I'm sure if you go ahead with everything, you will come to realise that in time. There will be no worries about learning the practical parenting stuff as you'll already know how to change nappies, feed etc. You are right in saying that you've already made the HUGE adjustment to parenthood from being childless (and don't underestimate the stress of that -you got through it).
Anyway, will stop waffling now. Your post says that your heart wants you to go ahead, and really, that's all that matters. None of the other stuff does. Best of luck.