The biggest drawback of house repair for such large areas is that it is not cost-effective. I would rather buy a sack of dry mortar (20kg C-mortar) and use it to smooth the surface. Once the mortar has hardened, you can apply regular wall filler, so don't apply the mortar too thickly as it will be difficult to achieve the correct level for the repair. It's good to start on a smaller scale to see the results, as it may require some practice if you're doing it for the first time.