Yes, HRH is probably the closest to US only a couple of minutes, PBH will take about 15mins to US and RPR is around 5 to 7 mins to IOA, there is the boat taxi from all 3 resorts as well. have a look on google earth if you have it.
Yes, the Hard Rock is about 5 minutes, the Royal Pacific is about 7-10 minutes, and the Portofino is about 10-12 minutes, but shorter if you cut through the Hard Rock.
We have walked from both the HRH and PBH but in the summer walking from the PBH seems like a trek thru the jungle - unbelievably hot! And we are people who will walk 10-15 miles a day while at the parks. The boat seems like a great option.