D&D 3/3.5, by design, changes roughly every 5 levels. You may find that your group becomes comfortable in one of those 4 quartiles, or you may find that your group enjoys the changes of pace that happen when moving from quartile to quartile.
You will likely find that access to a handful of spells (and to a lesser extent, some magic items) makes certain kinds of adventures (mostly "dungeon crawls") impossible. You will be able to identify those spells easily (they're the ones that the PCs "out of the box" of the dungeon map. By fiat, you can remove those spells, and that keeps the game nicely centered in adventures where the PCs can influences pretty much only those things they can see with the naked eye.
You will find that if some of your players min-max their abilities; especially the rogue and the cleric, they will create situations where the difficulties they need to face to challenge their abilities will have target values (DCs) much higher than those used against the rest of the party. That is typically mostly harmless, because you'll be able to see that coming, and scale the necessary challenges upwards to keep the game fun for them, without impacting the rest of the players much.
The key issue you will have to decide on is whether to use the baseline assumptions regarding the ability of spellcasters to make magic items. If you allow potions & scrolls only (which is pretty common) you will need to pay special attention to the equipment worn by the PCs to keep them properly equipped to face tougher and tougher monsters (per the Monster Manual). If you do allow the casters to create items, or you assume that magic items can be "bought" off the rack made to order, then the players need to take responsibility for dealing with their own equipment; if they fritter money away on things that don't keep them competitive with the escalating challenges, they'll pay the price.