you used to only be able to apply for a 60 day tourist visa, from UK, within 3 months of travel. I'd wait and see if they reduce the 60 day visa exemption back to 30 days. If you submit all the documents correctly, evisa is processed very quickly. Try applying 4 weeks before your travel date, if necessary.
There is a free shuttle bus between the 2 airports. Takes about 40 minutes, depending on traffic. Ask them to tag your luggage, rapid transit. Then it will get loaded last & come off first.