Yes, for playing through safari you just need to go to https://stadia.google.com
For your second question, that is something we all have to wait to see what Google announces in the future unfortunately!
At the Launch event at the GDC 2019 https://youtu.be/hl-Y1QVhmcM?t=1449 they totally announced that for the Future they have plans to bring up to 8k/120fps but no roadmap, so as @Matt1 said we can just wait for other announcements!
Yes, for playing through safari you just need to go to https://stadia.google.com
For your second question, that is something we all have to wait to see what Google announces in the future unfortunately!
At the Launch event at the GDC 2019 https://youtu.be/hl-Y1QVhmcM?t=1449 they totally announced that for the Future they have plans to bring up to 8k/120fps but no roadmap, so as @Matt1 said we can just wait for other announcements!