I recommend looking at the medal of whoever you are targeting
Most likely it will be the last major thing they accomplished so if it says something like skipper II dont attack them they have very strong forces
If it says something like greenhorn 3, turtle 1, or ferryman 1 they are likely to be an easy opponent.
I got this trophy with a little luck i had 2 defense victories and 2 offense victories in a row then used 90ish rifleman they are weak against howitzers (the land cannons) near the back of stages because of low health and they tend to group up but they will shred an island if you have something to distract the howitzers
Keep in mind destroying a command bunker will be an immediate win condition so if its close to an edge of the island just use a few boats and save your troops if you retreat with a star you still win
The second win condition is 50% destroyed so if there is an island dedicated to barracks and hangars i highly recommend attacking here first
If youre lucky and play well you can get all ten victories in under an hour i was able to do it without boosting my barracks because a rank 5 barracks will take less than ten minutes to train all the rifleman it can and that is roughly how long you should wait so you can train some boats, planes and i recommend using a med drop just in case things dont go well.
I also recommend not using rangers unless things are going poorly they are a nice emergency troop because they take forever to deploy