The key answer on the diner, dealing with a major theme of the movie, comes in the form of the quote of the old farmer (rancher?) who they question at the diner:
"Those men robbed the bank that's been robbing me for 30 years." (paraphrase)
These people hold some admiration for the bandits, and certainly aren't going to sell them out to the bank that's been bleeding them. They aren't bound by the letter of the law, but by their own personal, ethical codes.
[It's helpful to know the history of "bandits rob with a gun, bankers rob with a pen", featured in Woody Guthrie's "Pretty Boy Floyd", a song about a depression-era bandit hero. During the Great Depression, people couldn't pay their mortgages and were oppressed by the banks. Outlaws such as John Dillinger and Bonnie and Clydehttps://en.wikipedia.org/wiki/Bonnie_and_Clyde were folk heroes.]
The waitress's refusal isn't inexplicable either. She's attracted to Toby, and even though he gently rebuffs her, he still tipped her like $100. Her loyalty her is to the big tipper who is also a nice guy, not to the cops or the bank.
On number 2, maybe, but it would be hard to convict based just on thinking it was Toby's voice.
On number 3, they specifically only rob money from the trays because it's unmarked. The banker could be suspicious, but they can't prove anything. Also, Toby was advised to open up the trust account at that bank to keep things as copacetic as possible. (i.e. the greed of the banker/bank works in Toby's favor--they'd rather have the cash back in an account with their bank than get into a lawsuit with an unknown outcome. The bird in the hand over the possible two in the bush, so to speak.)
On number 4, the assumption is there is a reasonable amount of traffic. Texas is a big state and you're talking about fanning out in all directions. Even at a 50 mile radius, that's a huge amount of territory to cover. Toby didn't look suspicious enough to be detained.
On number 5, I don't have an answer, but as careful as Toby was trying to be, what's to have stopped him from buying the car through a 3rd party or from some source that's not easily trackable. They were old cars after all.
But the film isn't concerned with the legal aspect. It isn't at heart a police procedural--t's a Western, and Westerns are concerned with personal codes of honor. So it's really about the conflict between Toby and Officer Hamilton's individual codes.
Hamilton is presented as a competent cop, so if the evidence isn't there, we have to assume Toby, working on the advice of a lawyer, successfully covered his tracks.
Tanner's sacrifice of himself also probably contributes to Toby's free status at the end. His death gives the Rangers a partial win, and he can't finger his accomplice. (Tanner's self-sacrifice also arises out of his personal code.)
But, in keeping with the theme of personal codes of honor, Hamilton doesn't care if he can convict Toby in a court of law. Hamilton's code calls for vengeance regardless.
That's what the film is really focused on, and why they don't spend more time to get into the details of why Toby isn't arrested.