use regular post rather than FedEx etc if you can. I think laptops are still exempt from tax but if they aren't, FedEx etc are certain to attract the tax man
You may not have to pay anything. Got a very expensive Dell sent from the US. Insured. Zero tax or VAT.
Computers used to be exempt if you're not importing to sell. Probably still are, but check. Pre COVID-19 they could get sloppy about checking packages and you'd escape tax. Now they seem to inspect everything.
in general if they ISSUE the visa you'll likely get in. at the discretion of the immigration officer, of course, so be polite.
a) if you're talking about a tourist visa, they've been limiting the options for back to back TVs for a long time, but i don't know the current state of things.
b) for Non-B, they started discouraging the issuance of back to back non-B visas *before* the pandemic. they want you to go to get an extension in Thailand. and Chaeng Wattana is a pain in the ass, especially your first extension if you own your own company or work for a small company.
what happens next hasn't been announced, and it's kind of pointless to speculate beyond the general trend.