Most (but far from all) startups in Edinburgh are based in the Codebase building: https://www.thisiscodebase.com/. We also have a couple of unicorns that were started here, Skyscanner and FanDuel; Amazon and Smartsheet also have offices; and Rockstar North is where GTA is developed.
All of the above companies are within 10-20 minutes walk of the Edinburgh Waverley train station. Public transport is awesome mainly because the city is quite small and buses are frequent and cheap.
There are plenty of meetups too - see https://techmeetup.co.uk/ for the biggest general one, which is also live streamed. There are others on security, JavaScript, Go, Machine Learning etc.
If you like hiking/camping/hill walking then Scotland is a great country for you - you have a view of the Pentland hills from the city, and Arthur's Seat in Holyrood park right next to our parliament buildings. You can be in the Cairngorms national park within a few hours by car/train.
Upper end for Senior Engineer take home pay after taxes is around £4,000 pm. You could rent a nice apartment for £1,000 pm, but could get something small and habitable for £600.
Edinburgh is Scotland's most international city, which is a double edged sword as the tackiness of the tourist shops up and down the Royal Mile showcase. But there's lots of great things to do and see, and varied places to eat and drink. The University of Edinburgh is one of the UK's best (I recently walked past Prof Peter Higgs :) and students come here from all over. The Edinburgh Festival is (one of?) the biggest arts festivals in the world and runs for the whole month of August. The Fringe Festival is a world famous testing ground for stand up comics - there's a great Netflix special from Hannibal Buress about his experience of the Edinburgh Fringe.
Big downside to the city is that it doesn't have a tech sector as well developed as, say, London. Also for as stunning and booming as the city is, the weather is pretty bad especially owing to its unpredictability i.e. four seasons in one day. It's drier than most of Scotland but that's not saying much. It's cold and the winters have short days. The flip side is that a sunny summer's day will be one of the most enjoyable of anywhere in the world.
EDIT: and yeah, I echo other warnings about waiting until the Brexit debacle has concluded to see what things are like for the UK