Fischer esterification is an equilibrium, and separating rate from yield is the whole key to this question. The substrate controls how fast you get there and the catalyst amount does too - neither one sets how far the reaction goes.
SUBSTRATE: sterics dominate. The mechanism runs through a tetrahedral intermediate, so the carbonyl carbon goes from trigonal planar to crowded sp3. Anything bulky near that carbon fights the reaction.
Alcohols: methanol > primary > secondary > tertiary. Tertiary alcohols largely fail - under strong acid they ionize to a carbocation and eliminate to the alkene instead of attacking the acid.
Carboxylic acids: acetic and formic react readily; branching at the alpha carbon slows things sharply. Pivalic acid, with three methyls on the alpha carbon, is the classic sluggish case.
Electronics matter but usually lose to sterics. Electron-withdrawing groups make the carbonyl more electrophilic and speed attack; donating groups slow it.
CATALYST QUANTITY: a catalyst lowers the activation barrier for both directions equally, so it changes only how fast equilibrium is reached, never where it sits. Doubling your sulfuric acid does not raise your theoretical yield. A few drops of concentrated H2SO4 or a small spatula of TsOH is genuinely enough.
Using far too much causes real problems: dehydration of the alcohol to an alkene or ether, charring and darkening, sulfonation if your substrate is aromatic, and a harder workup. There is one honest caveat - concentrated H2SO4 is also a drying agent, so some excess can pull water out and nudge the equilibrium right. That effect is small and unreliable compared to doing it properly.
To actually raise yield, use Le Chatelier: flood the reaction with the cheaper reactant, usually the alcohol as solvent, or remove water as it forms with a Dean-Stark trap or molecular sieves. That is what moves the equilibrium. The catalyst just gets you there sooner.
