Just a few thoughts leap to mind as I read your request:
Yes, your stress will increase.
Yes, your daughter will get a little less of you, and will probably have to learn to share and help at an earlier age than a single child. She may experience this as a curse, but as with almost all changes in life, they also bring blessings.
Yes, based on (almost) every multiple-child family I've ever known, your heart has no limits on how much love it can produce.
Yes, your family will lose a little independence while a new baby grows through its first couple of years.
A sibling is NOT good for all children. This can be true continuously from infancy through old age, or only during certain periods of life. There are so many factors involved, that it's impossible to predict. I've known at least as many people (and I'm one of them) who would gladly do without the siblings they've been saddled with.
Alternatively, many only children are extremely happy being onlies. This assumes, of course, that they are getting the attention they need from adults, and opportunities to play and socialize with other kids of various ages. My daughter was a very happy only, and so is my grandson.
The last thought I'd like to throw in, a concern that helped me decide to stay with one child, is that more babies are being born than at any time in human history, and population pressures are seriously straining the earth's capacity to provide for all of us. We're producing pollution and garbage at an astounding rate. There are shocking food and water shortages that are being accelerated by economic pressures and climate change. Unspoiled nature is being overrun by humans, who are crowding out forests and other species. We're consuming natural resources at unsustainable rates. I've known about these problems since I came of age in the 60's, and they are all much more acute today. So I stopped with one child, for the good of all children.