The Max VAT rebate is between 11 to 13% if I remember correctly depending on how much the total bill on one single receipt and you have to be in time to claim the VAT at the airport as there are also opening hours for the VAT claim at different airports. You can only claim and the last port of departure. So I suggest getting to the airport early if it is the first time you are there.
After which you'll have to change to SGD and see some further loses on the exchange rate.
Actually, the 70-200 f/4 may or may not be a good option if you are looking to use it at the long end for nature. 300mm isn't much for wildlife especially in SG and with the f/4, the only TC one can use on a f/4 lens would be a 1.4x TC that gives you an effective FoV of 420mm and aperture of f/5.6. While using a 1.7x TC is possible on f/4 lens on a FX sensor, I have yet know what trade off are there when used on an APS-C sensor. For nature, I suggest the AF-S 300mm f/4D coupled with a TC-14E II and when used on an APS-C sensor, it gives you 630mm FoV. From there, for nature photography you must be ready to set aside time, quite a fair bit of time like 2-4 hours (incl travelling time) to capture something interesting. So, the more important question is do you have/or is willing to spend this type of time?
What you don't have now is a landscape zoom so you can consider getting the Tokina 11-16 f/2.8 II now and drop the 16-35mm f/4 VR or get the 16-35mm f/4 VR and a FX body from the money budgeted for the 24-70mm f/2.8. The reason I cited dropping the 24-70mm f/2.8 for a FX body is because the 24-70 is almost the same cost as a D600 if not more expensive and you already have a 50mm and with a 16-35mm zoom, the most commonly useful range of 24mm to 35mm is covered, leaving you with a 70mm not covered.
A pretty complete lens range setup for what you mentioned (minus nature) could be 16-35mm f/4 VR, 50mm f/1.x, 70-200mm f/4 or f/2.8G.
Thanks all for your insights and suggestions. I do general photography, macro, landscape, street and nature. I hope the 3 lenses together with my manual 105 AIS and 50mm prime will cover all my needs, except for the ultra wide end. Maybe should get the Tokina 11-16. I am deciding whether to bite the bullet and buy the 3 Nikon lenses in Europe. Making a trip to Europe soon and from tax rebates should save about $800. Regards.