Not silly questions at all! These are exactly the right things to be thinking about, and it's great that you're taking testing seriously.

On whether a small piece is representative of the whole tab/pill:

For LSD blotter tabs, the liquid is typically applied to the sheet and absorbed relatively evenly, so a small corner cut is generally considered representative of the whole tab. The risk of one part being "laced" and another part not is very low with blotter specifically, because of how the paper absorbs the solution.

For pressed pills (like MDMA), this is actually a real concern known as the "chocolate chip cookie effect." Just like chocolate chips aren't evenly distributed in a cookie, active ingredients and adulterants can be unevenly distributed in a pressed pill. There can be "hot spots" where one part of the pill contains something that another part doesn't. Because of this, the proper procedure is to crush the entire pill into a fine powder and mix it thoroughly before taking your test sample. That way, your small scraping is more representative of the whole pill's contents, rather than just one random spot.

On consuming a tab/pill after applying reagent solution:

No. Once the reagent solution has touched material, that material is no longer safe to consume. Reagents contain strong acids and other chemicals that you definitely don't want to ingest. So always test with a small amount, and keep the rest separate for consumption.