Hi A.,
It seems like you have a world of love to give to your kids. And that's wonderful. That's the most important thing. And I don't get the impression you've done anything really wrong or have done any harm. But, on the basis of the posts I've read, I did want to suggest a couple of principles.
1. Three-year-olds can't clean their rooms. Every once in a while, you'll find a 3-year-old who can, but those kids are rare cleaning prodigies. This is the age when she can start LEARNING to clean her room, but you can't expect real results for years.
2. I actually wouldn't worry about how many toys she has now. How many toys she HAS won't make her spoiled. The issue is how OFTEN she gets NEW things. And that should be very infrequently. Birthdays. Major holidays. And that's it. Show your love for your daughter by playing with her. Attentively. Creatively. Make the toys she already has magic.
3. Be sure to be tuned into her interests, even if they don't fit with the girlhood you imagined for her. It could be, especially if she has older brothers, that she may go through a tomboy phase. It's fine and wonderful to be thrilled that you have a girl. But she's not just any girl. She's YOUR girl, and that makes her one in a billion. Focus on what makes her special and unique, not just girly this, girly that.
4. Children need structure. They thrive on patterns and predictability. Having the same routine, day to day, makes them feel secure. When they get out of line, they need simple, unspectacular rewards and clear, predictable consequences. Offer a piece of fruit as a reward for being good. If she acts up, put her toys on the fridge. As soon as she shapes it up, she gets her toys back. That way, she derives power and control from being GOOD. It makes being good incredibly appealing.
5. Preschoolers act out in public. They all do. When my son (who's always been well-behaved) was 3, he once lay on the floor of the supermarket cereal aisle, threw cereal boxes into the aisle, and screamed because he thought a cereal had Buzz Lightyear on the box, only it turned out it didn't. BUT, the only way they can learn to behave is to go out in public. If you don't take her places, she won't learn the norms for being in those places. And when she acts less then perfect, every mom with an older kid will catch your eye, smile, and say "I've been there." Because we all have.
6. Your daughter might benefit from a preschool program, even if it's very part-time. Her big brothers can't always be expected to play with her (though they should do so sometimes, and they should tell her no nicely). She might benefit from making friends her own age. And you'll get to be part of a whole community of "preschool moms." None of whose children are perfect ;).