Lighting, Light Fixtures, Ceiling and Exhaust Fans - low volt transformers

I have everthing wired and ready for some low volt fixtures in my basement. My questions are, can I run 2 50 watt fixture off one transformer providing it has 100 watt rating +. Or do I need to use seperate transformers for each individual fixture. I want them on the same switch. Another ? i have is I need a 300 watt transformer. The lighting store only stock a 150 watt. Can I double up 2 150's to get the 300 watts needed. Sorry for what may be dumb ?'s but the low volt stuff I am just not sure about

Yes, you can run two 50-watt fixtures off a transformer rated for at least 100 watts. But no, you cannot run a single 300-watt fixture off two 150-watt transformers.