my experience with them was very positive. But yes, they will look for reasons why the applicant will travel back to Thailand. Being your girlfriend and you covering the trip doesn't cut any ice. They want to see her connections to Thailand. Reasons why she won't just go there and try to stay there. Job. Kids in school. Owning a house. Etc. If married it's much easier though.
VFS global offers several add-on services. For example documentation and filling out forms. Go look on the website. You are going to apply through there anyway.
there is absolutely nothing stopping you from entering from a different country than where the visa was issued. You could have an itinerary through multiple countries. But they require you to be present in the country you apply in.
told you what it actually happening, based on personal reports from people going through it. They want you to be present in the country of application until the visa is issued, and if they find that you are not, they will likely cancel the application without refund. That many people have done it without "getting caught" doesn't mean that is the way to do it. Just for example in Laos they require you to come pay at the embassy in person. Pretty sure that's to make sure you are in Laos and not trying to apply from somewhere else.
Did you already use the 60 day visit family extension based on being married? That extension is available once per entry. And it would allow you to both buy time to season your money, and also lets you apply again directly for the one year extension, without needing to start over with a new initial 90 day non o.