The nearest airport is Kolkata, though flying from Europe it is generally a lot less expensive to fly to New Delhi and take the train to Navadvipa. Flying from the west coast of America the price difference between New Delhi and Kolkata is not as great. As with all times of the year flying to India it is wise to book well in advance and book a return date.
Getting an India Visa is relatively easy. You can search for the web site of the Indian Embassy in your country, which will have the relevant details and downloadable forms. This should be done well in advance (4-6 weeks) especially if you are sending it by mail. The cost of the visa varies by country as does the length of the visas available. A six month tourist visa ($60) is adequate, though over time it may save money to apply for a five or ten year visa ($150, available in the US, may not be elsewhere). All tourist visas begin on the day of issue (not the day you enter India). For all tourist visas, the maximum period of stay in India is limited to 6 months (180 days). Visas which are valid for over 180 days (i.e. anything but a 6 month tourist visa) say that you must register with the Foreigner Registration Office within two weeks of your arrival in India. In practice however, you probably don't need to do this if you are only staying for a month.
In recent years there have been several devotees who have needed expensive medical care due to accident or illness which would have been covered by this type of insurance. The US State Department highly recommends travelers to obtain this type of insurance, which includes coverage for air ambulance back to their home country, regardless of their foreign destination.
Changing money in India is not too difficult and can be done safely at the right place.
Actually, coming from the west it's amazing how inexpensive India can be. Of course on the parikrama everything's included (except drinking water, snacks, and sundries). It is customary to make a small donation at each temple we visit (there are quite a few). There is no fixed amount for this, it depends on your means and generosity.
In the 2004 Vraja Mandala parikrama two devotees discovered that American Express traveller's cheques can be impossible to replace. Read about their tale of woe.
Thomas Cook cheques are also widely accepted, so I would recommend them instead.
Porters at the train station wear red uniforms and have badges that say "Porter". They are supposed to charge Rs. 40 per bag, but always want at least Rs. 50 per bag from a tourist or more if you clearly can't manage them yourself. You should fix the price before they touch your bags. I try to travel light and never use porters, though there have been times I wished I had.
Generally speaking, westerners don't like to haggle. We're from the fixed price, barcoded world. Haggling seems so... distasteful. Though it takes a bit of practice, it's not as hard as it sounds, and you're expected to do it. You'll get used to it in no time, and when you go back to the west, you may have to check yourself from haggling.
With all rickshaws, you fix the price before you get in which generally involves some bargaining. Tell them where you want to go and ask how much. The Hindi word for "How much" is "Kit-na?" As in "Alka Hotel, P-Block, Connaught Place, Kit-na?" (well, that's not quite right, in proper Hindi, it's "is ki kimat kya ha?" but "Kit-na" works fine). Being a tourist you will always pay more, but should not pay outrageously more. You're expected to haggle a little bit using the strategy described above. Knowing the going rate is key. Sometimes (not often) the rickshaw wallah will actually quote the going rate, in which case there's no need to haggle, jump in and say "chalo bhai!" (which can mean "Get Lost", but in this case means "Lets get going!")