Hi Janice,
Thanks fantastic news! I hope you have a great time - you're visitng two of my favourite cities in the USA!
In answer to your questions, as it is still an international flight we would recommend that you check in 3 hours before departure.
In terms of how much money to spend... North America has something to suit most budgets (and remember - food portions can be on the large side). I would recommend you budget as if dining out in the UK.
I can see that you have already booked some of the optional excursions, and if there are any others that you would like to do, there is time to book these before you leave so you don't need to worry about carrying the extra money whilst away
And then, it's all about souviners - I always save a bit of extra cash to bring some goodies home for friends, family and myself.
Hope this helps,
Julia