The Embassy website still only describes single entry and the online application also does not give the multi option.
Requirements listed there, updated August last year, are here....https://london.thaiembassy.org/en/page/spouse-and-family-visa Financial requirement is stated as "Financial evidence showing monthly income of no less than 40,000 THB (£1,000) or having the current balance of 400,000 THB (£10,000), e.g. bank statements, proof of earnings" , but it has been reported here they do not insist on that and will accept balance of GBP 1000.
One thing they do not list is for details of your flight from the UK to Thailand. For a non-O application in February they e-mailed me asking for this after my initial application had gone in online.