1. Subs are THE number 1 priority in any home theatre consideration for me. i would get two of the best subs you can get as they will add the most fun factor to any HT experience. You could get away with only one really good one if that's all the budget allows. Movies can have a lot of bass content that normal loudspeakers wont be able to reproduce. I had a couple of 2400 JTR Captivators which were incredible. You will only need moderately good mains, centre and rears with the subs doing all the heavy lifting for both movies and music. If you can build your own this would save a lot of money in this area. You need to spend a fair bit to get a sub that can do the job otherwise. I imported my Captivators at a cost of about $3k each so probably a bit too steep. If i were going to do the same again i would get one jtr orbit shifter which would be about $5k by the time it lands here. Otherwise something from svs would suit the budget and could probably afford two for around $2k if buying secondhand.
2. A good separate power amp and preamp is what I would recommend that can give the dynamics needed to light up the action on screen. I had a cary cinema 11a and an elektra power amplifier. probably a better preamp around now but that combo was awesome. Great for music too. The power amp wont date but the preamp features will. That combo would set you back around $2k. I would look for 5.1 or 7.1 and keep it simple to start. Otherwise an avr will do it all but may tapout when pushed. Hdmi output is all you need to get the best out of bluray so an older preamp would do the job. Emotiva umc 200 is another to consider and can be had for a couple hundred dollars.
3. Speakers. Get five or seven. I had both and didn't notice much difference between five or seven. go for something small but make sure they're matched. Should be able to get something for around $1k. With dual subs you wont need big floorstanding mains so save your money here would be my advice but get something good. Not sure what to recommend but ive had klipsch and have always liked them. The kg series which are older but never fail. Others might have better suggestions on this.
4. Bluray player sony bdp 370 at less than 50 bucks is great.
there you have it in order of importance. Good luck.