Jem's are great guitars. If your playing a Jackson now, a Jem is much more similar than say a PRS or Gibson. So you should be able to adjust with ease. But we cannot tell you if it's the right guitar for you because only you can decide that. So go find one a play it a whole bunch and then you'll have a good idea of what all Jem's are like.
Ok now that that is out of the way. It's up to you if you want to go new or used. New you get a brand new, unplayed guitar with a warranty. Used you get no warranty, played guitar but you save hundreds. I would go with used because you save lots of money and in a way it's more fun to buy used then new. Especially if you get a great deal. You will have to forgive me because I don't know the exchange rate from dollars is so I will leave that to someone who knows.
Now, What Jem to get? Well you have quite a choice really. Just look around Jemsite and you will see all the Jem's ever made. Then, I suggest trying to find the ones that look more visually appealing to you. Why? Because all the Jem's a pretty similar when it comes to the stuff that really matters. They all have great pick-ups, the all have the best trems, they all have great necks (however those very slightly). The big element that is different in Jem's is the neck joint. Older ones have a standard block neck joint. (I feel dumb because I don't know what they were called.
) Then the newer ones have a the AANJ (All Access Neck Joint). It allows smoother and easier acces to the upper frets. So that can limit your choice if it really matters to you. And again I apoligize because I don't know when the AANJ came into being.
If I were to recommend a model I would say go with a 7DBK if you want to spend less money or a 7VWH/7VSBL you have a bigger budget. The reason I choice these is because the older models I like are gaining value with time and seem to cost quite a bit. However it is up to you. So find a model you like visually and then go from there. I hope this essay helped. If school was in session I would probably turn it in.