KamnanT

I might suggest that if you have Thai visitors, you don't want to be storing your shoes in an "above door" shoe rack, particularly if they have to pass underneath it to enter/leave your house.

You say she has a US entry visa "for work" that is valid for 10 years.  Visas that permit paid employment in the US are normally not valid for 10 years - I think you must be referring to a B-1/B-2 visa that permits short-term visits for tourism or business.  A B-1/B-2 remains valid even if the passport it is affixed in expires. Your GF should be granted entry if she presents the expired passport with visa along with a current passport in the same name.

I don't know which bank's online banking you are trying to use, but Bangkok Bank's online banking requires you set up the payee's account details first, verified by one-time passwords sent to your mobile phone.  After the payee is set up, you can create a transfer transaction.

Assuming that you can collect all of the required documentation and get an appointment at VFS, this page gives you some indication of how long it currently takes to process a Settlement Visa application.  As of today, 22% of applications are processed within 15 days, 89% within 40 days and 100% within 60 days, so if your goal is to travel at the end of August, that's not an unreasonable expectation if you provide a complete application and satisfy the ECO of the bona fides of your relationship.  Your wife also will need to show that she is free of tuberculosis and has passed an approved English language test that certifies her ability to speak and understand English at the A1 level.

And don't, of course, forget the fee of THB 82,600 for the visas (THB 41,300 for each applicant).  There will be further charges for status changes once in the UK (e.g. conversion to ILR).

Yes, you will need a visa and you will need to obtain it in advance of travel.  You can apply at the Consular Section of the Chinese Embassy in Bangkok: note that this is not in the same building as the Embassy itself - the Consular section is in a building on the southwest corner of Ratchadapisek Road and Ratchadapisek Soi 3.  You can download application forms from this site - as you are applying outside your country of citizenship, you will need to complete both Form A and Form B.  I have a vague recollection of US citizens having to complete 2 copies of each form, but that may be outdated information.

There are at least three options available for processing speed: from memory, the "standard" application, which is the least expensive, takes 5-7 working days.  The fastest (and most expensive) "rush" option gets a visa in your hands the next business day.