Well, if you're going to move to a 125 in a few months, I'm not as worried about the anemone in terms of size. It will become quite large, though, so you need to plan for that when you're setting up the 125. Keeping a small tank is a great way to get into reef keeping, but they're harder to keep stable... you'll see the difference when you switch to the bigger tank. Remember, we're trying to emulate the ocean... with so much water volume the parameters basically never change... so we have to try to keep our parameters steady as well.
Right now: stability, stability, stability. Grab a notebook, test your parameters frequently, and write down the parameters each time you test. If you can get in the habit of doing that now, it'll be the best thing you can do for your tank. And of course, go slowly. That's going to be vital to keeping your anemone at this point.
Also, I'd think about not taking advice from whatever LFS you're shopping at... anemones and SPS require more stability than most other livestock (Some people recommend waiting as long as a year after establishing a tank to add SPS for optimal health. I personally don't wait quite that long, but just by way of making a point). Soft corals are much more forgiving.
For now, I'd reconsider on the SPS... the anemone's likely to be growing and stinging them before too long, and you don't want to lose them. If you really want to try corals and the anemone in the 12, go for something soft and inexpensive (so it won't be upsetting if/when it does get stung) like xenia or mushrooms.
Beyond that, what all are you feeding your tank, what supplements are you using, and what is your feeding schedule? Good luck!
