I am definitely interested in having this little one spend alot of time with me, but I have one major concern... we are foster parents and I currently have a little one (3 years old) who is quite aggressive. I often get kicked, hit, bit, etc... and I'm worried that if I am wearing the new one the poor baby will be like a human shield.
Oh my, that sounds really stressful! I have no advice from experience, but I would say that if you have the baby tucked up in a secure carry in a ring sling or wrap, it will at least be out of the toddler's range when you are standing up, and frankly you'll probably be able to better protect the baby than if it was lying around in a seat or bed where the 3yo could attack it directly.
Also, if you get good at babywearing, you can start safe back carries in some types of carriers around 4 months (when baby has better head control), and at that point it will be even safer.
I'm so sorry you have to worry about this, though, and I wish you the best of luck!
What Leigh said! At least the baby when worn will be on you so you can protect the baby instantly (your arms, standing up, etc). No worries of the baby being picked up, falling, etc. As far as to which carrier, check out the different types and see which one appeals to you more. A carrier you LIKE is one that you're more likely to want to keep practicing with. (Ring slings, wraps, mei tais, and SSCs)
You CAN wear newborns on your back but only with woven wraps. I would advise that if you want to do that to find a babywearing instructor or babywearing group since there are certain things you need to do to ensure safety and proper positioning. I don't have any experience with it personally. You can find groups through google searches (a lot have Facebook pages these days), thebabywearer.com, and babywearinginternational.com.