Its good you have direction and are taking control. Mediation is not required so if you are set on a divorce now then there is no need to go through it. I didn't even attempt mediation until 6 months after final order and clear break to sort the kids but it went nowhere. You can file online, tick the box for "no fault" and just get on with it. Solicitors should help through the process.
As for her comments around being unaware, its a way for her to avoid blame. She will say there were hints or comments but no actual accountability or communication. Men need clarity and clear comms, women in the most, don't provide that and work on innuendo and feelings from my experience. Never blame yourself for not seeing it coming. You are not a mind reader and she will have been stewing on it for ages in advance when she could have talked to you. Everyone is the victim in their own story and her friends and family will reinforce how brave she is to take this step.
As for financials, she will get to see balances as part of the divorce, you need to list all assets and debts on the forms and if she contests you may have to do a full disclosure. Be open and honest. Clear your debts if you have cash as it puts you on a clean slate and then when its divided its an easier path. Be prepared to split everything at least down the middle and if you earn more it will likely not be a 50/50 split. For the kids, if she agrees as part of the process on you having custody then it requires no mediation or court order. The solicitors will draw up the agreement and she will sign it and you solicitor will advise how enforceable it is. Follow their advice and honestly now is the time to just let them handle it. Define what you want and put it across via them.
Vent away and if you want any stories of the process and how it pans out drop me a PM. It will only be as difficult as either of you make it so be prepared for anything depending on when she realises what she is losing.
As for her comments around being unaware, its a way for her to avoid blame. She will say there were hints or comments but no actual accountability or communication. Men need clarity and clear comms, women in the most, don't provide that and work on innuendo and feelings from my experience. Never blame yourself for not seeing it coming. You are not a mind reader and she will have been stewing on it for ages in advance when she could have talked to you. Everyone is the victim in their own story and her friends and family will reinforce how brave she is to take this step.
As for financials, she will get to see balances as part of the divorce, you need to list all assets and debts on the forms and if she contests you may have to do a full disclosure. Be open and honest. Clear your debts if you have cash as it puts you on a clean slate and then when its divided its an easier path. Be prepared to split everything at least down the middle and if you earn more it will likely not be a 50/50 split. For the kids, if she agrees as part of the process on you having custody then it requires no mediation or court order. The solicitors will draw up the agreement and she will sign it and you solicitor will advise how enforceable it is. Follow their advice and honestly now is the time to just let them handle it. Define what you want and put it across via them.
Vent away and if you want any stories of the process and how it pans out drop me a PM. It will only be as difficult as either of you make it so be prepared for anything depending on when she realises what she is losing.

