Just coming to this thread now, I see you got some decent advice as well as comments from certain people who have a strong agenda against AI tools. I figured that fact may be relevant information for you.
Anyways, If you want to see what tools are available, checking dedicated AI threads (e.g., in Science subforum) may be more useful. It seems people interested in AI aren't frequenting this subforum too often.
AI Tools For Coding (For the essential game code and speed along development of the Alpha)
To some extent, ChatGPT may help. Not in the sense of automating code generation entirely or even in bigger chunks, but to help with the small things, like writing a small code snippet that you need. To see whether it's worth it: just try it. That's the only way to see if this improves your workflow. Make sure to give sufficient detail on what you want to be coded, and how. Use ChatGPT 3.5 for testing, no need to pay for 4.
AI Tools For 3D Modeling (Mainly for the random generation of Terrain like some of those blender tools)
My experience so far: 3D modeling with AI is 'feasible' but not really convenient at this point in time. Can't recommend this yet.
AI Tools for 2D Art Generation (Mainly to help come up with rouge ideas for concept art)
2D concept art & ideation is probably the most feasible item on your list. If you want to generate the art locally, use Stable Diffusion. Requires a serviceable NVidia gpu.
For starters see this UI:
https://github.com/AUTOMATIC1111/stable-diffusion-webui/
Just as a side note: Some styles, like pixel graphics, may need a bit more work than others.
Otherwise, if you are willing to use an online service: openAI's DALLE3 is doing pretty well. (Besides very good generation quality, DALLE3 would probably be easiest to use for people new to this, because it doesn't require that much "prompt-engineering". Simple prompts / requests in plain language work well and can be improved sequentially.)
PS: Music and speech generation are also possible, but I don't have any experience with those.