There is a set of Volkswagen 5X100 bolt pttern 16" steel wheels for cheap localy.  Want to put my winter tires on them for 'my '03 Legacy GT sedan.  Will they fit, I know I need16" wheels to clear the GT's brakes.

The VW center bore is larger which means these wheels on your car will not be hubcentric. May or may not be a problem. Why not just buy used Subaru steel wheels? 

Using non hub-centric wheels can cause wheel balance issues. Have a tire shop balance the wheels using a lug-centric adapter and they should be fine.

I've been running chrysler steels on my Impreza for the last few years. You should be fine.

They will work fine.

 

lugnuts align the wheel.

 

IF there was force being transfered to the hub centre ......it would mean your lugnuts are not tight enough.

Tighten the wheel nuts (very gently at first) using a 1-3-5-2-4-1 pattern. That will help centre the wheel correctly.

 

The (horizontal) offset should also be checked, and compared to the existing Subaru wheels. Offset is unlikely to be a problem, but in extreme cases could cause the tire to rub against the suspension.