Photography is about creativity. Not everyone will like what you have taken. For me I'll get the 28mm as I find the 50mm more suitable for portraiture. But there are people who use the 50mm for landscape shoot too. It's all up to you. Do take note of the f-stop which will affect the bokeh.
Yeah. The 28mm lens with your A100's 1.6x crop factor may not be wide enough scenic or interior shots.
A medium telephoto (200-300mm reach) might be useful too if you'd like to take portrait photos of people, activities/antics of locals and tourists, and animals from a distance. Both for convenience, safety, and not to alert the subjects to your presence to preserve their 'natural' pose or behaviour.
You might want to save up first before buying those expensive lenses. Maybe you might want to bring a small tripod, if it's ok with you. Or find some steady objects to let you rest your camera and take the night shots. Another thing is to increase the ISO, but it would increase the amount of noise. Just my opinion.