IFR rating
I think I can put a perspective on this, having had a fixed wing IFR rating since 1983 and a helicopter IFR rating since 1987, currently holding (Current) Command Instrument Ratings in both fixed wing and helicopter, and instructing instrument flying on both categories. The hours requirements for either category (In Australia at least) mean that you will have to do more training and prove your competency on both. That is, if you start with a fixed wing rating, you then have to do 20 hours on category, that is on a helicopter, of instrument training in order to sit the test for your helicopter rating and vice-versa. Which one you start with probably does not matter. In fact, it is easier to learn in a fixed wing because of it's inherant stability compared to helo's, and the procedures and processes are still the same. As for the question regarding the instrumentation, you will find some schools doing IFR training on incredibly basic aircraft, both helicopters and fixed wing. You have to sit the test on an IFR certified aircraft, so you will have at least the basic IFR fit. So what if it does not have an HSI/RMI/TSO GPS or whatever: when you fly an aircraft that has one you arrange to learn about that and away you go. I constantly fly aircraft that have instruments/systems I've nover seen before: read the manual, get some instruction, and practice until you are competent. In fact, it's like the Tiger Moth training question, learn to fly without ll the fancy gismo's and you'll be a very good pilot: add the systems later. Learn to fly on a glass cockpit super performance aircraft, and you'll never be a good Tiger Moth pilot. Same principle applies to IFR.
It must be good to be in a situation that money is no object! Biggest recommendatino for you: spend heaps of time an a synthetic trainer, with a good instructor supervising, getting your IFR procedures perfect. You'll be a much better, and safer, IFR pilot for the practice.
Hope this helps.