Which UK tourist visa should I apply for?

I'm a non-US citizen with a green card wanting to go on vacations/visit friends and family in the UK.

I know I need the standard visitors visa but I have a few questions.

How long is the standard visa given for? Can I travel multiple times within that duration? I ask because they have different fees based on how long of a visa I want.

Edit: I found out that its for six months, still not sure if I can make multiple visits though.

You can also apply for a long-term visit visa if you can prove you need to visit the UK regularly over a longer period. You can stay for a maximum of 6 months on each visit and your visa can last for 1, 2, 5 or 10 years. Fees You must pay £85 to apply, plus an extra fee depending on the length of your long term-visit visa: 1 year - £324 2 years - £324 5 years - £588 10 years - £737

I might need to go a second time this year, so I am really trying to decide if its better to apply twice, or try to convince them to give me a longer term (1 or 2 year) visa. Would it be harder to get the long term visa than the short term one?

Also I think I should wait to buy tickets/hotels till I get the visa, but some people insisted that it might help with proof of my trip for the interview. Is that correct?