Uphigh I would be surprised if a baby really got totally ignored, very worrying if the baby was adopted or birth child.
If you want to explore this a bit more can you say why you want to adopt, as opposed to having another child by birth?
There are lots and lots of threads on here for people wanting to adopt with birth children. If you start by looking at these you will get some ideas and can come back with a few more questions, maybe?
Certainly lots of people adopt with birth children. Realistically a baby you adopt would be unlikely to be a new born s they would be maybe 6 months to a year old. So you birth child would need to be two and a half or three. In many ways they would be getting to the 'preschooler' stage. Still very young but able to amuse themselves alone, play, maybe share, wait when necessary etc.
I know someone who had a birth child of 17 months when her second birth child was born. That is mega close. I think a two to three year gap would be more doable. I have almost a 6 year between my birth dd (10) and adopted ds (4). A big gap is better. But adopting a young child when your birth child is younger may be a slightly smoother transition than I had as my dd was very jelous having been the only one for 9 years.
Also, it is about energy, your energy! If you can cope with two under 5 or two under 4 or two under 3 that is something you may know. Can you get a friend round with a young baby and spend an afternoon together and see how it goes? Actually, that will tell you very little! adoption is about uncertainties but I am sure you could make it work if you wish to.
Good luck, ask some specific questions and someone wiser than me may come along. 