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This link will answer your questions.
http://phytosphere.com/soilphytophthora/soilsterilization.htm

To help prevent clogged holes, you can place a piece of window screen or mesh over the holes. Add a layer of gravel, broken terra cotta pot pieces, or even wadded up newspaper to the bottom before adding soil. Yes, you can use packing peanuts. This will assist with draining. Then, add some sand or vermiculite to your soil to loosen the soil and help it to drain better.

Here are a couple of articles that you might find helpful:

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/types-of-potting-soil.htm

https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm

You should be fine. The non-topsoil parts of your mixes will break down over the years so your bed will sink ever so slowly. You can add a 50:50 mix of compost and topsoil (the type I buy has a bit of sand added to topsoil) over the bed to top it off when needed.

There is no risk of burning plant roots when liming; however, it is most effective if worked into the top 7 inches of soil where most of the plant roots are. Lime is slow to act and will take up to a year for full effect. If dug in this fall, there will be a substantial difference by spring. Get a soil test a year after application. I suggest you submit samples to your state's extension service. Results include recommendations to correct pH and nutrient problems specific to the plants you will be growing. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/adding-lime-to-soil.htm
Clay soils need significantly more lime to affect pH than sandy soils. I hope the recommendation you were given takes this into consideration. 180 pounds sounds like a lot but I don't know what pH you are aiming for.

I like to use the solarizing method! This article will help: https://www.gardeningknowhow.com/garden-how-to/projects/how-to-solarize-garden-beds-to-eliminate-garden-pests-in-the-soil.htm

It would not hurt to add a little of both, but if you had to choose, then compost would be more beneficial. I like to add in the fall to give it time to break down a little in the soil.

This article will give you a little more information on the benefits of using compost: https://www.gardeningknowhow.com/composting/basics/garden-compost-benefits.htm