I had my DD in Jan this year. After lovely pregnancy - with a bit of MS and lots of aches and pains - I ended up needing an emergency c section (after attempts at ventouse and forceps). I'm really thinking seriously about having another and trying when I get over the year stage. I don't want my DD to be an only child, but as I'm nearly 40 I don't want to leave it too long.
Start trying again as soon as you are able to. Seconds can take longer than firsts to conceive, and if you do need to go down the IVF route, you'll need as much time on your side as possible. As for coping... we all worry about that. But somehow we all manage! You'll be fine. Good luck!
I'd say go for it - plenty of women have babies in their 40s these days and so long as you think you can cope then no reason not to. Most women have a bit of a wobble about how they will cope with more than one, but once the baby comes you somehow just get on with it same as when you went for 0 to 1. So long as you are aware of the increased risks of chromosomal issues such as Downs and know what you would choose to do re testing etc (very personal decision) then 40 shouldn't put you off - but of course do remember that most babies are born healthy too, your odds are not that bad for a problem. Also I believe slightly higher risk of twins with increasing maternal age...worth considering I guess!