First things first, the moment we think of going to Thailand, we think of VOA (Visa on Arrival) or the new E-VOA (Electronic Visa On Arrival).
The Thai government in order to boost tourism, have done away the visa fees for VOA. So, if you are landing in the city where you would spending your first day, then you are good to go for VOA. But, incase you have a connecting flight: eg. going to Phuket and you change flight at Bangkok, you would need to get the VOA and also clear the immigration at Bangkok itself.
Now, I would suggest if you are planning in advance, there would be no harm in taking the Visa before leaving and being Hassel free.
Incase, you are planning it and have left it all to last minute. Do not panic. You can still get your Visa on Arrival, even if the transit time between the connecting flight is around 1.30hrs. make sure you have all your details on a piece of paper already (flight number, number of days you are staying, hotel bookings and addresses, passport number, your passport size photograph) and then rush towards the VOA counter, fill your form and ASK for EXPRESS SERVICE. It's from the left side along with the group counter, where you will have to pay 200/- TBH per person and in 5 mins you get your Visa stamped and you are good to go for immigration clearance and towards boarding your onwards flight.
Now once the Visa planning is done, next question is how to explore the cities.
Phuket: is best explored on a two wheeler. Hire a two wheeler which costs around 250/- TBH per day.
For Airport transfers, you can either take the busses or the mini vans or Pvt cabs. You can also book them on Klook app.
Bangkok: use the BTS. Easy and convinient from one place to another and for exploring and going in the area, tuk tuks are not a bad option.
Clothes: anything you are comfy with. No one is bothered about what you wearing. If ladies re wearing very short shorts or skirts with off shoulder tops, they can get wrap around at the Big Buddha, where you are expected to cover them. Light coloured and quick drying clothes is always helpful as you would be using the sea, beaches and water activities in Phuket.
Charger: the Indian chargers work well everywhere. So not a problem.
Currency: I feel it's a good option to split it between cash and forex card. Definitely carry some loose TBH in cash for VOA, as they do not accept the cards or any other currency. There is no charge in using the forex card with TBH, when used on a POS.