Our boys are 2.5 years apart, and DS1 was a very high needs, challenging child with some issues until he was about four. After DS2 was born, I did not find it difficult to care for the new baby - he was pretty easy - but I had some extra challenges to consider in caring for DS1.
Probably the most difficult thing for me to deal with was that he was a dart/run/climb guy, and once I had a big belly, and later an infant with me all the time, chasing him became impossible. The logistics of keeping him safe became much more difficult. When pregnant I could not go as fast as he could and was also afraid of injuring myself. Once DS2 was born I could not leave him to chase DS1, and did not want to take the risks of a flat-out run with him in a carrier either. My main solution was to keep DS1 strapped into a stroller with a 5 pt harness with DS2 in a carrier until DS1 outgrew the running. There were places this didn't work though. At the grocery store, he had to be strapped into a cart with a bench seat and a seatbelt, because he couldn't fit into the regular cart seat anymore - his legs were too long - and I could not lift him into them anyway - so grocery shopping became completely dependent on me getting one of those bench-seat carts. If I got to the store with both kids and one of those was not available, I had to either leave without groceries or wait for one of the carts, with a seatbelt that was not broken. I also stopped taking DS1 to parks for a long time, because he would take off, so I felt like we could not safely go to a park unless I had a friend with me to watch DS2 while I caught DS1.
So the new baby was the easy part - it was adjusting how I cared for the older child that was the biggest challenge. The hardest age was when DS1 was not quite done running away or climbing random structures in stores at almost four and DS2 at 18 months was so big that carrying him on my back was hurting my knees, feet, back, and hips. I did use a double stroller for a while but that was many pounds of kid to be pushing around and too big for some stores. Things got much easier after DS1 quit running and climbing everything. DS2 started walking, and he would run sometimes, but never as far or as fast, and never did the random climbing thing, and I did not have as many worries about chasing DS2 because by then DS1 would follow me.
Now they are 4.5 and almost 7, and they are each other's best friend and constant playmate. It was hard but worth it, and I am glad they have each other.