Thought answer should be straightforward but was told that frontier is different.

After flying first leg of two leg outbound, my second leg was cancelled by Frontier due to mechanical/maintenance reason (not weather/ ATC issues) which was confirmed in an email

Rebooking link had technical error as it was giving choice to change flight from origin rather than from transit point onwards.

After 1 hour in line, agent told me that since there is only 1 flight per day to the destination from this transit point and next day is full, I am better of applying for refund and purchase a ticket myself on other airlines.

Purchased a last minute basic economy with one further change to eventually reach destination 13 hours later (given 5.30 am departure, had to spend night at airport)

Question:
What is realistically expected from Frontier?

They have put down in writing that they cancelled connection due to maintenance issues

Their website cud not rebook.

Agent told me (verbally) that no alternative is available for next 48 hours and arrange something myself.

Serves me right for opting to fly the misery Airline but what refund I Shud expect? (Entire outbound leg or they will somehow deduct cost of flying first leg and leave me with 5 USD refund? How about baggage fee?)

Any compensation given the overnight misery/delay and have to buy new tickets?

TLDR;

When frontier cancels second leg of two leg outbound due to maintenance reason (in writing) and agent unable to rebook for couple of days requiring one to complete the journey using separately bought last minute ticket, what is realistically expected from Frontier? (What Shud I ask for)

They are not required to reimburse you for a ticket you purchased from another carrier if you choose not to fly F9. All they are required to do (both legally and from their Contract of Carriage) is refund the fare you paid for your original ticket on F9. On a one-way connecting ticket, they should refund entire ticket even if you have flown the first leg. You should assume that is all they will do for you.

If you continue to pester them, they may offer you a $100 voucher (pretty worthless since it doesn't include taxes, CIC, seats, or bags, but YMMV), and if you pester them some more they may up the voucher to $300 - again fairly worthless. They could offer a $1 million voucher and it would have the same value since it can be used only once and only covers what they determine to be the actual airfare.

Using the vouchers subjects you once again to the misery of flying with Frontier.