Buy it at a local pharmacy. Or mail order if the price is even better. (yes of course you can post meds, but you don't want them sent from UK and stuck at Thai customs)
I get my heart meds locally. eg Ranexa 1,900 baht for a box of 60. It's the most expensive meds I take. Most are 100-400 for a month supply
And for what it's worth, in your position I would pay more than minimum wage. You want to create some loyalty, with a feeling they are quite lucky to be working for you, rather than having to find a replacement every few months.
The Thai Embassy in your country would process a non-immigrant O visa. Most require you to apply online, but all the requirements will be on their website. Each embassy seems to vary requirements slightly, so go by the one in your country, who will be processing it for you. This allows you 90 days from arrival (and one-way ticket would usually be fine).
Once you arrive, get an address (I used a one-month hotel booking, but it may only take you a few days to find somewhere to rent) open a bank account (use an agent for this as the banks seem happier to get the kick-backs agents give them!) Once you have a bank account and an address, you can apply for a 12- month extension. And for your wife, a Dependant visa.