Well there aree practically endless choices and combinations of gear for 5k. And since you don't know anything about it, there's going to be a lot of learning on all of it.
I would suggest a bad ass pc running only music software, with a nice soundcard, a controller, and good monitors or decent ones at least, and a good premic source if your gonna use a mic on anything. That's where the 1402 comes in handy. Because it has some of the best mic pre's for the money and it also serves as an outboard mixer. With a multi input soundcard you don't have to use a mixer but I prefer it.From there on out, what can't be taken care of with software or the controller/workstation, can be bought cheaper as rack units controlled by existing gear.
Your best bet is to put in as many hours in a music store as possible. They'll normally let you play around for as long as you like. Find the gear you want and then get it as cheap as possible and if you buy new, your gonna lose money. You can save a ton if you buy used. Just make sure it isn't used hard.
Try to decide if you want a workstation controller like a kurzweil k2500s, korg triton or
yamaha motif 8. Or maybe virtual analog synths like the lead 3, virus, waldorf, ms2000 or novation. Certain synths in both categories can be found faily cheap on ebay, depending on the model.
I personally would want one of each. Either k2xxs/triton/motif8 as a main controller, then right above it a nord lead 2or3/ms2000/virus indigo2/super
novaII/waldorf Q+. All plugged into a nice motu or delta soundcard. If your gonna use mic's add a mackie 1402 mixer and a shure sm57 or something like that.
I would think a workstation and one virtual analog synth coupled with cubase sx, or what ever software, would be enough to keep you busy for 2 years if your a fast learner.
Just start out with one synth workstation or virtual analog first, and while your learning about it and how to play keys, you should be able to formulate a plan as to what you want or need from there. Just go to a music store that has any of the models I mentioned and play with them and see which ones you like best.