Optimized tables and limit and any other tips on dynamic performance

I am working on things to improve the performance/load time of pages on my website.
The limit statement I used this to test worked great in my app (navicat) but it does not work on my actual web page.
Queries in PM. Is the LIMIT doing the same thing as selecting the # of records to return in the repeating region?
Again, just searching for assistance for best performance.

I have noticed that the more similar queries I run each time the results are returned faster. -

I also want to optimize my database tables and need advise on best practices and anything at all that will help.

Do join statements have a significant negative impact on page load time, number of records, number of columns in database?
I am trying to educate myself so I can make intelligent choices to minimize page load time.

Limit statements are automatically added when you do repeat regions to match the number of rows you are using. Adding indexes on any columns in joins can really help when it comes to speeding up results.