First Landing (soft) as Canada PR and going back to US on F1 visa

Hi,

I got recently approved for Canada PR and I am currently a resident of USA and an International student with F1 visa status and STEM OPT Work authorization.

I want to do my First Landing in Canada as PR (soft-landing) and spend a week in Toronto and head back to US. I am currently working on my OPT authorization in US and I recently switched jobs and my New Employer is flexible of me working remotely from Canada for couple of days.

I have a few concerns to be answered:

1. I am thinking to fly to the closest Niagara Border airport at Buffalo (BUF) and cross the Rainbow Bridge on foot as it is the only bridge that allow Pedestrians. I will be carrying my Passport and CoPR and other documents. Is it okay if I land in Canada first time on Foot and go through the CBSA immigration? My cousin will be waiting on the Canada side to pick me up. They can't cross border as they don't have visa to enter USA. Any risks in this approach?
2. Since this is my first time PR landing, I have read that I can't cross the border in a Public Bus service (Flixbus, Megabus) as that is considered Commercial Vehicle and I need to have either a PR Card or PRTD, or I will be denied boarding by the bus driver. Is this information correct? I plan to take Uber ride till the Rainbow Bridge USA from Buffalo airport and walk over the bridge into Canada if the Bus service is not an option for me.
3. When returning back to USA, another friend of mine will be dropping me at Buffalo airport as he is a Canadian citizen. So will I be scrutinized at the US CBP while going back with the current immigration situation. I will carry my i20 with Travel signature issued by my University DSO/ISSO, Employment letters from Current and Previous Employers, recent pay-stubs and other documents. How to avoid potential risks and what things to keep in mind to avoid any issues while entering US?

Appreciate any insights. Thanks.