My partner was driving last night when a police vehicle behind…

My partner was driving last night when a police vehicle behind him put their siren on and pulled him over. He has described the ensuing scenario as such:
Two officers approached his vehicle:
Officer: Have you been drinking tonight?
Partner: No
Officer: Do you have any illegal substances in the vehicle?
Partner: No
Officer: You look pretty stoned to me so I'm going to ask you again because I'm going to search the vehicle anyway...Do you have any illegal substances in the car?
Partner: Ok - I have had a puff on a joint just before and there might be some crumbs in this tobacco pouch [hands officer a tobacco pouch visible on passengers seat - vehicle is owned by my partners brother who had been in the vehicle prior and it was at this previous destination that the joint had been smoked]
Officer: Im going to search the vehicle [open door and and opens glove compartment] are there any needles or anything else in here i should know about? Have you got a bong or anything in here?
Partner: No that's it
[at this point the other offer conducted a breath test which had no register of alcohol consumption]
Officer: Right well we're going to take you back to the station

At no point was my partner swabbed. At the station he was issued with a notice to attend/appear in court and the "evidence was seized" and he was issued with a receipt stating that he had had one gram of marijuana seized and that he could apply to get the evidence back for independent testing.

It is my understand of Queensland law regarding drug related sentencing and penalties that a first time offense of possession - particularly of an amount of one gram of this particular drug requires that officers:

"offer someone the option of diversion if they are found in possession of up to 50 grams of cannabis. This is the only state in which diversion MUST be offered to a minor cannabis offender..The diversion includes a mandatory assessment and brief intervention program. Only one offer of diversion is allowed per person".

Can you please advise as to:
1) wether he has been "formally charged" - hence the notice to attend court?
2) "diversion" is an alternative to "conviction" of the charge and this is then decided upon by a judge at the court proceedings?
3) is "diversion" now not an option as it has already progressed to a future court appearance?
4) is it advisable that he seeks formal legal representation for his court appearance?

He has no prior charges or convictions related to drugs or alcohol.
Your assistance with this matter will be greatly appreciated as my partner has experienced minor issues with in the past due to an undiagnosed mental health condition which he is now undergoing regular treatment and counseling for. He has been exceptionally well for almost a year now and this incident is causing extreme duress and uncertainty and I wish to ensure he has access to the best advice and support and information.