Yes, you should.
I have used Audiolense 7.1 with JRiver since before JRiver offered its own convolution (VST plugin prior to that). It works!!!
1. Yes, you will most probably end up with a superior room correction. One important aspect is that you are able to get the target response to your own liking.
2. Soundcard with in and out, and a calibrated mic+mic preamp. In/out must be on same hardware to get consistent and low latency.
3. Sky is the limit, but I doubt you will find mic and and preamp for less than a few hundred $$.
If you plan on doing 7.1 setup, good frequency resolution (=many filter taps) and with active cross-over to sub, you can easily end up with a 15 path convolution filter. This is relatively cpu intensive, and I would be a bit pessimistic about using anything but a moderate to powerful htpc. But I may be wrong.
I found that my old three-core AMD Phenom could not do convolution blu-ray video with RO-HQ standard. I now use a i7, JRiver benchmarking around 4000.