Is south side 50 feet? And west side 30 feet?
All the directions are auspicious as per vastu and at the same time, each direction will have certain principle to follow, while constructing a house.
For south facing house also, if entrance is towards SE direction, it's considered to be good.
If you divide your south wall in nine equal portion from SE to SW, first 4 portion are good to have entrance. 4th portion from SE is the best for south facing home. 1st to 3rd are also ok. 5th till 9th, we should avoid as an entrance for south facing home.
If you can send plan of your house, better analysis can be done on that and other areas of your house like bedroom, kitchen, balconies, toilets etc. All these things do mater, not just the entrance.