Go ahead and get a bag of the Durabond 20.....it will put some pep in your step......once you understand you better be ready to use as soon as it is mixed..... 🙄-durabond 45.
-buy a metal square patch from the drywall aisle...fill the hole with insulation if you wish.
-laminating plaster with 1/4" drywall is a great fix...but pay attention to your trim profiles...may make more trouble.
-for fixing lots of cracks in a plaster wall and not screwing up trim details...glidwall is a helluva a product...but there is a learning curve.