Best local LLM/agent stack for 128GB M5 Max Mac Studio?

I have a new M5 Max Mac Studio with 128GB arriving today. We bought it primarily to run local LLMs on sensitive client data for my wife’s consulting business, and I’m trying to figure out the right stack before installing everything.

The goal is more than local chat. I want an agent capable of coding, browser automation, logging into websites, pulling data, analyzing it locally, and working through multi-step tasks. The Studio will also be her primary work computer, so ideally the LLM doesn’t monopolize all 128GB.

Currently considering:
Hermes Agent
Qwen3.8-Flash-Next
Possibly the MTPLX Optimized Speed build
Tailscale for remote access

Where I’m confused is the inference/server layer. I originally planned on LM Studio. I’ve used Ollama before, but it sounds like people are moving away from it. Now I’m reading about MTPLX for Flash-Next, and I don’t understand whether it replaces LM Studio/llama.cpp, works underneath them, or is something different entirely.

A few questions:
What model would you run for this use case? Is Flash-Next the obvious choice on a 128GB Mac?
LM Studio, MTPLX, Ollama, MLX/llama.cpp, or something else?

Is the MTPLX Flash-Next build
mature/stable enough for everyday business use?

Am I missing anything?