In FF1 NES, WSC and PSX on Normal difficulty, your amount of MP is quite limited, so with healing, you should always have many Heal Potions with you (I always have 99 of them). I also use Mage Staff, Zeus Gauntlet, Black Robe and other things like that to cast Fire/Lightning/Ice2 and other spells like that, and Heal Staff or Heal Helmet to cast Heal1 on everyone.
In FF1 PSX on Easy difficulty, however, you'll have loads of MP. 9 is the max MP for each level in PSX Normal (and NES and WSC), but it seems to be 99 or so in PSX Easy. I'm only on level 17, but my White and Black Mage have MP for 30+ level 1 spells and even 10 MP for level 5 spells, and I'm only at Melmond, going to fight the Vampire next. Normally you'll have about 2-3 MP for level 5 spells, and you'll need to save about all of them to the battle against the Vampire, and later, the battle against Lich.
How is it in DoS? The leveling-up and cost system seem very similar to the system used in FF1 PSX Easy, but the MPs are now different. Instead of having separate MPs for each level, you'll have common MPs for all the levels, and higher-level spells take more MP to cast, just like in the newer FFs. In the original versions of FF1, you could go ahead and waste all your Cure1 spells but still be able to cast spells like Holy/Fade and Life2. In a system like the one in DoS, that clearly isn't possible anymore as if you spend all your MP casting Cure1 spells, you won't have MP for any other spells anymore. So how much will you have MP for spell casting in FF1 DoS when compared to other FF versions, such as NES/WSC/PSX Normal and PSX Easy?