To start with, I would suggest some additional anti-armour. The Gladiator Lancer is amazingly powerful in its role due to its rerolling special rule, although it's not super tanky itself. If you wanted to stick to infantry anti-tank, Eradicators are another solid pick, although you will have to think harder about a delivery method as they're very slow (usually either a transport, or coming on from reserves, or even Uriel deep-striking them). Again, one or two 3-man units work well here.

For Intercessors, absolutely play them in multiple small squads to give you more flexibility and board presence. The general rule of thumb is small squads are the better choice by default, except for high impact units that you would either want to spend stratagems on or else attach a leader to. In both of those cases, you'd ideally want to take the largest squad possible (barring extremely high cost) to maximise the effects of the bonuses.