While an I7 CPU might be desirable, a fast I5 processor will be plenty adequate for editing. I would recommend 16GB of RAM. If you can afford it, consider an SSD for your OS and applications - perhaps 250GB, with a 1TB or larger SATA hard drive for storing you photos/images. You will need a 64-bit OS. A separate graphics accelerator board (as opposed to integrated graphics) with at least 2GB of video memory is desirable. Most new machines will have a DVD drive (perhaps with BluRay as a not-too-expensive option), USB-3 ports, and a 1Gb/sec (GigE) Ethernet port as well as an N wireless adapter. Those are the basic specifications, and hopefully you can use your existing monitor (assuming you purchase a desktop) to save $. You may instead choose a laptop, but if you do, you'll probably want to use an external monitor for imagery editing. Btw, I have built a number of AMD-based machines (as opposed to Intel CPU-based), and they have some very competitive processors, but I have not used AMD CPUs for imagery editing, so someone else will have to comment on whether the AMD architecture is equally suitable for these type of applications. I have not suggested a Mac (although they are great for this type of work), because you're familiar with Windows and you won't be able to buy a new Mac with this level of performance with your projected budget (but a used machine may be an option).

As said by others, use the money for something else, you already have lenses that will do the job nicely. Do you have a garage? Found that I had much more room there than in the house. Go to youtube and you will find lots of videos that will be of help. They cover everything from one light set-ups to two, three, four, etc. light set-ups. I also have an open concept house (kitchen, dining room, living room all open to each other) and have had people stand in front of the living room fireplace and taken the picture while standing in the kitchen.