My pregame thoughts about GOTM21:
General
The big question is how isolated are we? We might be separated from everyone by water, might have just one local rival, or might be connected to many Civs by land. I don't have a guess. Exploration to find out is an urgent priority.
Food will be a priority. What we see at the start shows a very limited amount of food. If there's a river or lake nearby we can improve the food situation.
At large map settings research is going to take some effort. But Monarch level and being scientific does mean that it will be possible to get ahead in research and to get a fast overall tech pace if we want it. Slowing the tech pace will also be possible - this map's settings make either approach viable.
Opening moves
I'm going to start by moving the worker west onto the lambs. If that reveals a food bonus then I'll move the settler NW. Otherwise I'll settle at the start position.
Initial build sequence
I don't think a granary is an immediate priority with this start. The first town will run out of food if it grows large. It has only two food surplus per turn. Doubling that with a granary would gain just two more food per turn. Pumping out a settler will also (presumably) gain two more food per turn from the town it creates. Pumping the settler is cheaper and faster. So at least at the start I won't worry about granary, I'll build some warriors to go exploring and then aim for finishing a settler as soon as the town reaches size three.
Research
I plan to start by researching Writing at maximum speed. I'm not sure how much faster I can get it than the 40 turn minimum. But any gain I can make over that I want to. (I'm going Predator -> Space so I want a fast tech pace for sure.) My reasoning on going for Writing first:
1) I don't need Pottery quickly since I won't start with a granary build.
2) If there are neighbors around, Writing will be a good tech for trade.
3) If we're isolated on an island, getting to Map Making ASAP is a priority. So Writing and Pottery are the first techs to research. Given point (2) above, might as well start with Writing in case we're not alone.
After getting Writing, if we don't have neighbors it is an easy choice - go for Map Making. If we do have neighbors, it depends on how many and what their situation is. I might go for Map Making anyway, or might trade for earlier techs so that the AI goes for Map Making and then research something else to trade for Map Making later.
Hoplites
I don't plan to build many of these unless defensive action becomes necessary. I prefer to build offensive units. I may use a few Hoplites to trigger a Golden Age though I will try to defer that until after switching to an advanced government.
Wonders
At Monarch level it should be possible to build an early wonder or two. I think the Great Lighthouse could be especially valuable on this map. Colossus might also be helpful. The problems with building wonders will be:
1) 15 other Civs. There will be a fair bit of competition for each wonder and for any given wonder there will probably be one or two Civs building it in cities with good production.
2) With 15 rivals, and a high tech pace (not inherent in the map but I'll be trying for a high tech pace) wonder cascades will be common.
3) Our initial growth seems likely to be slow, making it difficult to get cities started on big projects soon enough. I'd like to have cities working on Forbidden Palace, Great Lighthouse, and Colossus. But it seems unlikely I'll be able to dedicate three cities to such projects soon enough.
Palace jump
Setting up for a Palace jump will be a high priority for me.
Although corruption will be lower than usual (large map settings and we're a commercial Civ) there's a good chance that geography will limit development around the capital. And therefore that a second productive region will be a priority.
Since the coastal start position isn't ideal for the Palace, building a Forbidden Palace a bit inland and jumping the Palace could work out well.
If the game develops such that a fair bit of early warfare makes sense then I might change my mind on this and try for a leader to hurry the Forbidden Palace somewhere, leaving the Palace at the coastal start position.
Miscelleneous
I expect that galleys will play an important part in the game. I'm nervous that there may be many squid. In case of this I plan to build early galleys in pairs, in separate coastal towns. One galley will start exploring first, as bait for the squids. After it has been out for a short time, the second galley will leave the other town and hopefully will have some safe time to explore - with luck the squid will be converging on the first galley.
As usual when playing a scientific Civ I plan to build few (if any) temples. Libraries will be a better way to generate culture.