I have just had DS2 two weeks ago and have a DS1 aged 11, and a DD aged 14, DD is in foster care but adores her little brother, wouldn't put him down, FC said she was surprised as DD is not 'one to show her feelings or be so loving'
DS1 Is fantastic with DS2 and it brings tears to my eyes to see him with his brother, very loving and caring.. he also is of an age to understand how much time DS2 will take up and that he is not forgotten, he does know how to express any wish for more attention in his own way but so far we are doing ok.
Also have a DSD and DSS aged 6 and 7 respectively, they are over the moon with baby also, i am waiting for DP's oldest DD to get in contact, she is 13, he is dubious about it but i have a one track mind in thinking sod what their relationship is ect ect, she has a right to contact with her brothers and sister.
I'm sorry for the apparent hijack but i wanted to explain everything before telling you, i think you will be ok, you obviously are a good mum as you have posted this question, caring about how your DS will take this is the first step.
Be open about the time baby is taking up, ask him for help, but not OTT or he may resent doing so much, there is a balance and you will find it i'm sure.
But i think you will find DS is over the moon with new baby and IMO it's a good age gap with less likelihood of jealousy, and less work for you as you don't have a demanding toddler and a new baby winners all round lol
Oh.. congratulations and good luck xx