Swapping a tub for a walk-in shower is the most requested bathroom project we do, and for good reason: it makes the room feel bigger, it's easier to step into, and it's the upgrade that pays off if you plan to stay in your home for years.
Decide on the threshold first. A low curb is the simplest build; a curbless shower looks cleaner and works for aging in place, but it requires the floor to be recessed or the drain to be planned very carefully. Both are doable in most Portland-area homes, but the answer changes the scope.
Waterproofing is where a shower succeeds or fails. The tile you see is not the waterproofing; the membrane and slope underneath it are. A properly built shower has a continuous waterproof system from the pan up the walls, a drain that actually drains, and ventilation sized for Oregon humidity so the room dries out.
Pick your tile, glass, fixtures, and niche locations before demo, because those choices determine where blocking goes in the walls. A good contractor will walk you through every one of them during the estimate, and the whole project usually finishes in a week or two once materials are on site.