When to ignore the iOS/Material design UI guidelines?

I am currently helping out my company with the UI/UX design of apps, and having no experience and prior knowledge, I find myself stuck between whether to follow the guidelines or not.

We're beginning to adopt the card design from Material designs guidelines, but I find that there is too little space for too many items. Our app specialises in travel, and these are a few problems I've met:
1. Name of place too long. Material design states that the title has to be 24pt. I think the guidelines say I shouldn't shrink the words, and I feel that I should keep it to a single-line.
2. The padding between the image and words (16px top and bottom) would lead to the phone only showing 1 card at a time, which I think is too long.

My question is when can I ignore these guidelines, or do I follow the guidelines only when I use the native elements (like bars)? The most common example is game apps where it contains no iOS/Android elements.(Is it called custom?). Especially for images, I do not now how much padding I should leave, but sometimes I use 8px and sometimes I use 15px (for iOS) and 16px (for Android)

Another question I would like to ask is, currently, I am being tasked to replicate the design of iPhone to both an iPad and iPad Pro. I could not find any guidelines for iPad, so what I did was I kept the same padding and enlarged the text and images. My problem is Sketch does not enlarge the text (as they are in pts), so how does a designer decide on the text size on the iPad? Is there a definite size for both iPhone and iPad, or is there only a minimum and the size can be decided based on preference?

I do feel that it's inefficient in creating a design for iPhone and iPad, plus doing it for Android too, and with so many phone models, it seems unrealistic. I would like to know what would a designer do when creating designs for both OS with different phone sizes.

Thank you.
-Kei