A lot of this depends on the specifics.

Do you need to be in-office for a full 8+ hours or can you work from the train on WiFi/hotspot and just be in office for like… 6 hours? (That could be the difference between a 6:30am train vs a 8:30am train, and getting home at 6:30pm vs 8:30pm)

Will the dates/times be fairly set and reliable, or will you have to switch it up? (If you buy Amtrak tickets to Trenton you can shave off 30+ min each way. But you would want to buy them far in advance)

Ewing is a little too far from the train station though, so it would make it very complicated. Probably not worth it.

To answer your question, yes it boards from the same place as domestic flights. Same TSA process as domestic flights. No extra checks (on the departing EWR side) other than a passport being required rather than a drivers license.

Double check - airlines may have slightly different boarding or checked bag timelines for international. But otherwise you don’t need to add much extra time over any other flight you would take out of EWR. It’s not much different than flying to Denver.

There are different levels to bidets.

An entry level bidet that doesn’t use electric (like a $40 one from Amazon) isn’t very difficult. If you can build basic ikea furniture you can install it. You basically just unscrew your toilet seat, install the bidet under it, put the seat back on, and then swap out a few tubes in the back of your toilet.

If you want a fancier one with a heating element it depends. With that you are typically replacing your toilet seat (check the size). You need electric, possibly at a voltage that your existing bathroom outlet might not have (if it’s even near the toilet). That veers into professional territory. But if it works with your existing bathroom infrastructure it isn’t too much harder than the basic ones.

It’s been a few years but I remember WiFi at the university was also free for X number of days per month, and buildings like the student center are open and have tons of seating. Assuming you are of student-ish age.