If you can understand a workshop manual and have some basic tools an
engine is no big deal..
Change
oil and
fuel filters is pretty straight forward and with practice can be done in minutes..
water pump">Raw
water pump impeller is 8 screws on the face pull out the old push in the new screw face back on..
There's also tricks if your
fuel fails, blockage/whatever that will have your
engine running again in 10 minutes on fresh fuel.. a 10 litre jerry can and some hose direct to your
fuel pump for an
emergency.
These are all things one learns on the go..
I started enginless, then outboards and did not have a
diesel till my 7th
boat.. my first one over 25ft.
The reality is much less daunting than you imagine unless your all thumbs and two left hands.