I'd like to change my Tourist Visa to a Non-Imm based on marriage. I have 11 days left on my TV and was planning on getting it extended sometime this week.

It is my understand that I need to have at least 21 days left on my TV to change it for a non-o, would the extension of my TV for 30 days be sufficient?

Also, does one need to show 400k at the time it applies to change the TV to non-o? I might need to wait 1 month before I can transfer the funds by swift to my account here in Thailand.

It all depends on where you're applying. Here in Phuket they ask you apply 3 weeks before the visa expires. Policy tends to be a bit flexible though so you might be Ok.

The 400K is needed when extending your stay for 365 days. So technically it isn't required.