for sizing, then order 2 pairs, one half size up and one a full size up. Most decent on-line shops ( and Hokas only stocked by decent shops, eg Castleberg Outddors ) will give you a refund when you return the pair you don't want as long as not been worn outside.
It does cost you the return postage for one pair, but you do get to try both sizes for a few hours walking around the house ( or even on a treadmill ).
Obviously check with shop first that they are Ok with this.
Apart from "Race against previous workout" any of the Garmins will do what you want. Look at the Garmin website at the Forerunner watches to see which do "Virtual Racer" for racing against previous workout. Certainly the 610 and 910 do, but not sure if the more basic ones do or not.