1-4 can be done without issue in DL, let alone done in DL + myth + CT gear. The wisest investments are those from the highest tiers of coil if you are not already regularly clearing t4/5. The person who says start with things that drops in T5 is the one to listen to, because better than DL makes a difference in there.

I'm a fan of the sword upgrade. For things like dreadnoughts, knights and soliders (who you'll need the extra emnity gain from flash on), and rooks you cannot have too much damage, even if its only a minor increase. If a dreadnought has 1% HP left, 1% that you could have done with an upgrade, and gets to eat some bugs, or has 1% left and gets off a lucky cleave while your mages are distracted with bugs. . . more damage is good, and the sword is a T5 drop as mentioned earlier.