it is 3 working days now, public holidays and religious holidays aren't counted. So if you submit your paperwork the day before a public holiday you can't pick up your passport for 4 days. If there are no holidays or weekend days in the three days that you are doibg your visa, submit paperwork on day 1 in the morning, collect paperwork in the afternoon of day 3
Vientiane is still a relatively easy Embassy to do a Thai visa. About a year before Covid they changed to an appointments only system. When I went in November 2022 there were about 6 other people applying for visas, it was literally deserted. You do need a copy of your bank account showing that you have maintained a balance equivalent to 20,000 baht for the previous 3 months. It must be printed out and submitted with your application-you can't just show it on a mobile banking app. It can be in a foreign or Thai bank account. You also need onward accommodation receipts. I showed receipts for 4 nights accommodation and a bus ticket to Bangkok and they were happy with that. You can do printing outside the Thai Embassy to the right of the gate if you need to print off any of these things. It is a 3 day turn around now ie lodge on the morning of day 1, pick up on the afternoon of day 3. So be careful of weekends, Thailand public holidays, Lao public holidays and Lao office holidays or you could find yourself (like I was) stuck in Vientiane without your passport for an extended period.
You can fly to Luang Prabang from Chiang Mai. Or take the slow boat from Huay Xai
no, you do not need a Thai bank account. Your home country account is OK. I did a tourist visa in Vientiane last month. You need to be able to print off 3 months worth of bank statements which show that you have maintained a minimum balance of money equivalent to 20,000 baht in your account for the last 3 months. You need to submit this proof as part of your application pack. So opening a Thailand account now wouldn't meet the requirements for a tourist visa at the Thai Embassy in Vientiane. This is why you use your home country bank to meet the requirement. Go on to the Vientiane Thai Embassy website it explains there what you need. It is easy to do yourself. You don't need an agent to help
There are two different financial requirements required for doing a visa run to Vientiane. You are correct, that to enter Thailand by land border, or plane you could be asked to show 20,000 baht in cash or an equivalent amount in foreign currency, a bank statement or proof of the amount in a banking app is not accepted as financial proof.
To get a tourist visa at the Thai Embassy in Vientiane now, you need to print off 3 months of bank statements as part of the application paperwork. The bank statements need to show that you have maintained a minimum balance of 20,000 baht in your account for the last three months. Showing cash or a banking app balance is not accepted. I successfully obtained a tourist visa in Vientiane last month. I used my Thai bank account, however there were others there applying for tourist visas who were using their home country bank accounts