My recommendations would be a minimum of a 6.5 x 24" ruler with 45 and 60 degree markings in colors that work for you. I personally would like an 8" x 24" ruler but have not found one that I'm willing to part with the $$ for yet. A self-healing mat if that is not what you have. In the largest size you can afford. If you have a coupon, a 12" (minimum) rotating cutting mat if you do many HST's. Otherwise no particular need for that.
I'm not a fan of specialty tools for the most part. I do have a tiny little metal 'ruler' that has little 'legs' on it for 1/4"; 5/8"; 1/2" and I forget the 4th measurement. I think I paid about $2.50 for it. Nice little tool to double check measurements. I do have a couple of specialty triangle rulers but that's about it. I've not had a need for other specialty tools other than the above that I've not been able to manage with my normal rulers/tools.
My only other recommendation - buy all the same brand rulers of varying sizes as you go along. The measurements will then be consistent among them if you decide to change ruler sizes during the various stages of block/quilt construction. Otherwise, use the same ruler throughout your quilt construction to make sure your measurements are consistent throughout your quilt.