Hi OP, the thing with adoption is the journey is generally long - so you have plenty time to sort out your feelings and work on stuff.
Nothing happens overnight.
We will finish stage two in November which will be a year since we started. Don't worry too much about all the abbreviations you will hear.
It takes a while to get used to the whole idea too. We have an 11 y/o daughter already - but even so we had to adjust to not having another 'birth' child.
Adoption is not a 'replacement', it is just different.
Having said that, I get where you are coming from on the failure part. I am generally fairly high achieving in my professional life - and have had some less than glowing interactions with the 'state' over this - and confidence takes a knock. The thing is, if we get as far as being adoptive parents, we will need resilience and strength, so I like to think of the whole process as a test.
Unlike a pregnancy, where (ideally) the outcome happens come what may - adoption is a bit stop/start, and that can be disconcerting.
I remember our first social worker (we are on our third now) telling us "Do not put your life on hold" - and I wholeheartedly agree.
Good luck, and keep coming back to this board - you will find it a help.
But, as well as that, try to remember to have a life too :)