Wow! I am in a very similar position to you in that I work full time while DH is a stay at home dad. We have a DD who is 2.6 and have been trying for DC2 for over a year with 2 mcs in that time.
I sometimes have similar worries such as how well DH will cope with 2 and although he wants another DC, he wouldn't be devastated if we didn't/couldn't. Sadly because of the mcs and the stress that is associated with early pregnancy (for us), he only wants to try once more, so this is my last shot.
I'm sure part of my desire for another child is hormonal - I'm 36 and I, like you, worry that time is starting to run out. I also want a sibling for DD as I really don't want her to be an only child. Plus after my mcs I just have a 'need' for a healthy child.
Like you, I wish I could stay at home more with DD and I only had 6 months mat leave because we needed my salary. If we have another, I hope to have 9 months off work!
If I do get pregnant now, DD will be over 3 by the time DC2 comes, so she will be at preschool, which will make it easier for DH. In fact since she was 2, she has been going to a playgroup 3 mornings a week, which helps DH and gives him more time to do a bit of freelance work and just have some time to himself. Maybe your DD could go to a similar group to take the pressure off your DH a bit (round here the child has to be 2 to go to such a group).
The way I look at it is that I will regret it if we don't try for another. We may not get there and if not, there are some pros to just having one child, but at the moment I can't help hoping we'll have another.
Good luck with your decision. Sounds to me like you want a DC2 - you can always work on your career afterwards, but you don't have the luxury of time to delay TTC really (sorry). I've sort of got a similar career dilemma, but have decided to move jobs after DC2 (hoping I get to have DC2!)