Yes, you still need a total of 75 infusions, so infuse whatever you want to complete after you've gotten to a stopping point on the attributes you actually want (weapon-depending, accuracy is not necessarily a bad stat to substitute with, it can potentially free up acc in other parts of your build).

It DOES consume alex per meld, but if you do your daily expert, you'll always have an alex per day from that quest alone. At the moment, i'm sitting on 77 alex and 3 extra maps I don't know what to do with (maybe if DRK has a relic/zodiac...), so you won't be wanting for more alex. If you are, there are a multitude of ways to acquire more (allied seals, alex maps with soldiery, FATE farming with Nexus and up).