Welcome aboard. You're not the first Captain to come from the 9.
If memory serves, the stock Roadster is already over your 150+ hp mark at 160. Of course, that's at the crank.
You can lower the rear by 1 in with some Ikon shocks. I actually have a pair of chrome shortys that have about 5k miles on them. Let me know if you are interested and we can work out a deal.
We have a number of darksiders (car tire) that have attempted to mount 250s and it is a very, very tight fit. If you want the fat look, you can mount a 240/50 ct to get the affect. I have a 225/55 on mine and it certainly gives the big tire look.
Can't answer your question about the front.
As far as opening her up to breathe, the biggest and most costly restriction are the pipes. You really have to do something about them first. Any intake mods will get wasted unless you do.
Once you take care of the pipes, the triple K&N intake mod is cheap (~$100 or less).
I could suggest an alternative to the side mount plate since you will run into legal troubles depending on the states you ride through. I have mine relocated up above the taillight on the rear fender. Easy install and fairly cheap (~$60 including new turn indicators).