Well, since you cannot legally drive once reaching 70 hours on duty you will be in violation if you drive after 5 hours of duty time on Tuesday. Yes, you can take a reset on Monday. If you start the reset Monday you will be ready to roll at 05:00 Wednesday or after 34 hours, whichever comes last, with a fresh 70 hours available. Or, if you took Sunday off you would be good to go at 05:00 Tuesday or after 34 hours, whichever came last, with a fresh 70 hours available. And again, the 34 hour reset is optional. It is not required. If you worked exactly 8.75 hours every day you would never exceed the hours in any 8 day period.
One more scenerio: If my duty is from Friday (12pm) to Wednesday (10pm) - 69 hours. I took rest. Can I start my next duty on Friday 12pm? Is it legal?
It is legal because you have met the requirements for a reset. From 10pm Wednesday to Noon on Friday is 38 hours so it meets the minimum 34 hours required for a reset. It also meets the requirement for two periods between 1am and 5am. Since you say you started the previous Friday at noon there is no possible way it does not also meet the requirement for 168 hours since the start of your previous reset. So yes, it meets all the requirements for a 34 hour reset. btw, I feel like I'm taking a test.