Ian,

I'll give my opinion on a couple of your questions -

Nothing wrong with going in August, it will probably be hot and smoggy though!
Worth seeing - Empire State building, Central Park, Times Square, Statue of Liberty and Elllis Island, Circle boat trip around Manhattan, Ground Zero, Grand Central Station, Rockefeller Centre, Haarlem

Spending money - totally depends on what and where you want to eat. It's not cheap but portions can be much bigger than the UK! Personally, for attractions, food, drink etc I would be taking as much as possible but at least £500 (that's without any shopping)!

Use the subway to get around! It's very safe (much better than London) and very convenient....albeit a little confusing how the subway maps work! Or walk of course, it's a very safe city to walk around.

In the States, waiters and waitresses often work for no basic wage, they only get tips so please bear that in mind. If you get decent service then I think it's reasonable to tip 15% of the bill, I would not tip less than 10% if the service was reasonable. I have never 'not tipped' in the USA, even with mediocre service to be honest.

They normally add a bit of sales tax to things you buy - can't remember the %, it's not much

Don't spend all your time around Times Square, yes it's something to see but just like the West End of London you'll pay tourist prices for everything, there are some great bars and restaurants in areas like SoHo, Tribeca and Greenwich Village.
I always recommend 'Arthurs Tavern' in Greenwich Village for a great night out, a fantastic little place, loads of atmosphere, live music, great service, it's brilliant. Stays open way into the early hours of the morning.

You'll need to do a search on shows available, you may be able to get discounted tickets online before you go

Hope that helps

TC

Just to throw my two penn'orth in ('tuppence' - 'two penn'orth'.... oh never mind!):

Re: must-sees, ditto to the previous poster; I would add, The Empire State Building FROM the Rockefeller Center ("Top of the Rock"). Also, you mention "we" - if your travelling companion is a lady, and one who enjoys shopping, I would definitely recommend Macy's department store (34th St) as somewhere which is not wallet-cripplingly expensive. Don't forget to take your passport and collect your 11% tourist discount card from the information desk inside the store I also enjoyed the "Foods of New York" walking tour which I did in Greenwich Village district, a lovely area which felt more 'normal' (i.e. real NY-ers living there) and less 'touristy' (i.e. surrounded by shops selling cheap plastic souvenir tat).

You mention how much money to take - as a reminder, there are ATM cash machines on almost every street corner, and in places like cafes and newsagents, as well as regular high-street banks. I was able to use my regular debit (Maestro) card to withdraw money, and got a better rate of exchange than the one in the UK at the time. It might be worth only taking a small amount with you, and withdrawing what you need over there.

Re: tips, I added a basic ten % (cos it's easy to work out ), and then a bit more on top depending on the quality of the service, and what I had on me in small change. Seemed to work OK (no-one seemed offended at any rate). Tipping is expected, so technically you do "have" to tip, or risk being thought of very badly!!

You do have to bear in mind the sales tax added to purchases at the point of payment, on top of the advertised/ticket price. I think this was the case for both 'shopping'-type purchases, and also things like meals/drinks in bars & restaurants (someone who can remember better might state otherwise though - happy to be corrected ).

Re: Broadway shows - I'm not sure if I'm allowed to post a link to a website, but if you Google "Broadway Box" this is a website giving reviews and advance purchase ticket discount codes for all shows on- and off-Broadway. If shows say 'sold out', you can still maybe get tickets either from the TKTS booth in Times Square, or by going to the theatre where a show is playing on the day of a performance - I did this and got a ticket for Wicked (lunchtime matinee show) at 10.25am the same morning, excellent seat, FABULOUS show and didn't have to pay any online ticket agents' exorbitant booking fees

I second the recommendation to use the subway, I found it very easy and felt a bit less like an obvious tourist once I'd got the hang of it.

Hope you have a fantastic time