You should always prioritize the upgrades that unlock new ships for OSRS gold obvious reasons to ensure you're getting it right. I believe every upgrade is worth it (except in cases where that you own more than one upgrade, which you are able to unlock all of them but you can only have one activated at a time so pick wisely).
The crew I'm talking about is that I have 4 bureaucrats (well the ideal thing is to have the best ones available at any given time, but I'm not sure of the names of the others so I chose bureaucrat - which is basically the team member who increases the numbers of other crew members) Crew members; And then 4 Morale, 5 Seafaring and four Combat crew members; 4 unique crew members (the ones who unlock by special trips, like those of Feral Chimera)
The crew configuration has always worked for me, but there's likely better setups. I'll likely get rid of Merchants and Merchants shortly and will soon be able to get more specially-designed crew members, or something, because honestly I very rarely use Merchants. I used them only for gathering trading goods to make armours.
Regarding Captains, I never cared much about the Speed rating. I currently have 1 Morale, 2 Seafaring, and 2 Combat Captains of the highest level available to me at the moment. (actually I believe I have unlocked one of the new tiers recently, but I'm not able to locate any new Capts yet)
With eoc, weapons are considerably more important than abilities in determining the amount of damage you can cause. Choose between Strength or Attack to buy RuneScape gold train without affecting the other.