I'd hardly call Draw Upon Holy Might a sub-par spell, especially for a fighter/cleric. It boosts all your physicals, and gets more powerful as you level.

You'd never need to allocate that many spell slots towards it anyway, since Strength is already the easiest stat to boost in the game. Especially for fighter, since the game throws so many potions of giant strength at you.

You don't need that many spell slots allocated towards Hold Person or Slow Poison. You're unlikely to fight more than a few groups of powerful humanoids in a day. The only part of the game where you'll be getting poisoned many times in rapid succession is Cloakwood, and by the time you get there antidotes are pocket change anyway. Through the rest of the game one or two spell slots allocated towards Slow Poison are sufficient.

If you're good aligned, which is recommended for a new player, you'll get a couple free casts of Slow Poison and Draw Upon Holy Might a day anyway, freeing up even more spell slots to be used as you please.

Gold is hardly a concern. Strength or no strength you'll rapidly make more gold than you could ever hope to spend, and the gold you'd make off those heavy items is negligible in the big picture.