how far by walk

You want to go walking from the airport to your hotel? The airport is far from Shinsaibashi, so its not something doable. but to reply:

A slow normal walking speed is about 3 kms an hour. This is a speed that you lets you tackle gentle hills without becoming short of breath of becoming tired even when carrying a lot.

5–6 kms an hour is usually typical of a fit person who wants to get somewhere quickly. Most fit hikers I know will maintain this speed for gentle slopes but usually end up puffing for more difficult hills.

To go to Dormy Inn Shinsaibashi from the Kansai Airport (KIX), is roughly 46km. So you would probably take around 15h or going fast, around 8h.

I recommend going by train. Here's a route for you: https://goo.gl/qNUrku
Going by train would take you only one hour.