I am an English as a second language student so that is also a barrier I am facing.

One of my friends suggested that one may face difficulty in learning LSAT without achieving 27+/30 in TOEFL Reading.

Should I wait until completing core curriculum before continuing to PT?

Definitely. You need to understand the basics of LSAT, learn how to tackle different types of questions, and train on by-type problem sets to master them. Only then will moving on to PTs to apply what you have learned helpful.

LSAT is hard. Unless you devote hundreds (thousands, very likely) hours, it's difficult to make any progress. There's no magic pills.

You are now possibly not understanding the whole LSAT thing. Don't worry. Spend your time learning every single course in Core Curriculum, and reflect, review and revisit whenever necessary, make sure you understand (almost) every bit of every video you watch and every post you read.

Another thing is, if you are using English as second language or foreign language (like me), you might have to focus on learning the English language itself before trying to learn LSAT, for obviously most students taking LSAT are native speakers, and LSAT assumes that you have a high-level mastery of the language.