Hi there
There is a 17 month gap between my two girls, so I understand your concern completely
It is not as bad as you fear, but I am not going to sugarcoat it, you will be busy! And there will be days where you feel you can't keep both happy. It is important that you have a good support system, and it seems like you have that box ticked already, which is great
Make special time for your 1st born where you just spend time with her alone, even better is someone else can look after baby for that bit of time in another room so you are not distracted.
My first LG did not want to hold her sister, she just touches her cheeks, head and feet, which for some reason are very interesting to her. You will just have to be careful that she does not clamber over the baby, my LG does not hurt her on purpose, but at that age they climb over everything and can accidentally step on a little arm or leg. So never leave the two alone in the same room.
We also had the baby "buy" our LG a gift, but I am not sure she fully understood the concept, though it does not hurt to try this.
I am lucky in that our second LG is a good sleeper, much better than my older one. The second one is generally easier.
So in summary, you are in for a busy year, but it is not impossible to manage.
Most people don't want to be an only child (I, for one, cannot imagine life without my brother), and a siblling is the best gift you can give your child. They may not always appreciate it now, but they will in time