First off, 270 ac isn't that small, we just get used to hearing about or hunting on 6000+ ac properties, I grew up on a dairy with nearly 200 cows and our place was about that size. With that said, it is still way too small to run a bunch of different exotic species unless you're willing to spend big time $$ feeding year round. I would only pick one other animal to add to the mix, and axis would be your best bet. One fact that you need to realize is that if you add axis or any similar species you are most likely going to negatively affect the performance of you whitetail unless you are willing to feed a bunch, and even then you may still impact your whitetail numbers and antler quality. A good rule of thumb if you want to grow your huntable numbers quickly is for every 1 mature male add a minimum of 5 females and at least 2 spikes/immature males.
Something to consider before introducing any exotics is the quality of your fences. When we bought our current place 7 years ago, we added fallow, axis and blackbuck after a year or so, the majority of our fences were in very good shape with real 8' deer proof fence, but we do have a mile plus section that is two 4' fences wired together that is over 20 years old. We lost 9 of 10 axis does that were likely getting run by coyotes that ran into the corner where the two 4' sections and an 8' section meet and broke the wires between the 4' pieces and escaped. Exotics will run the fences when you introduce them for a fairly long time and getting cornered by dogs/coyotes is a real possibility so your fences need to be in good shape before you turn any exotics out. Another consideration is predator control both prior to introduction and continuously after, any newly introduced specie is going to be easier pickings for coyotes and bobcats than your current whitetails are, so spending a little time and money trapping ahead of time with definitely help protect your investment.
Something to consider before introducing any exotics is the quality of your fences. When we bought our current place 7 years ago, we added fallow, axis and blackbuck after a year or so, the majority of our fences were in very good shape with real 8' deer proof fence, but we do have a mile plus section that is two 4' fences wired together that is over 20 years old. We lost 9 of 10 axis does that were likely getting run by coyotes that ran into the corner where the two 4' sections and an 8' section meet and broke the wires between the 4' pieces and escaped. Exotics will run the fences when you introduce them for a fairly long time and getting cornered by dogs/coyotes is a real possibility so your fences need to be in good shape before you turn any exotics out. Another consideration is predator control both prior to introduction and continuously after, any newly introduced specie is going to be easier pickings for coyotes and bobcats than your current whitetails are, so spending a little time and money trapping ahead of time with definitely help protect your investment.