You should absolutely at least get your keybinds for your spells (ideally all of them, but at least he ones you are using 90% of the time on a fight). The most common ones should be the easiest to cast (i.e. without using modifier keys).
Also, you should get an addon or some macros which autocast, for at least 2-3 of your spells, which you can easily use WHILE you’re moving with WASD (i.e. without needing to stop pressing any particular movement direction). You want to bind your defensive magic dispel, and 1 or 2 of your instant casts. For Holy paladin, I recommend Cleanse, Holy Shock, and Light of the Martyr. This allows you to move for mechanics while also continuing to do things.
For instance, my main healing spells are assigned to “1-6”: FoL, HS, HL, LoD, LotM. #6 I have assigned to a cooldown, which is currently Ashen Hollow.
Then, I assign the SHIFT+“1-6” to cooldowns; AW, HA, Aura Mastery, and LoH. CTRL+“1-6” are assigned to various defensives: BoS, DP, DS, BoP, BoF. Also, I have my Beacon of Virtue assigned to “Z” since it also needs quick access (Divine Steed and HoJ also falls into this category of needing quick access. I assign the middle mouse button to my interrupt on all of my characters; Holy doesn’t have one, so I put HoJ in that slot)
For melee attacks, I have “R”=Crusader strike, SHIFT+R = Judgment, and CTRL+R=Hammer of Wrath.
I have vuhdo, and I have the mousebinds set up:
Left click = select target (no cast)
Right click = Light of the Martyr
Shift + Left click = Cleanse
Shift + Right click = Holy Shock
Most of the other spells in your toolkit won’t be a hinderance if you have to leave WASD to cast them.