googlebot reads code from top to bottom and does not look at pages like humans do. it is best to place your important stuff towards the top of your code.
as for heading tags: many, many years ago google placed alot of importance on h1 tags. then webmasters realized this so they started to keyword stuff h1 tags. google quickly realized h1 tags were no longer an accurate signal. so google placed less importance on h1 tags and started looking at h2. guess what? that also got abused and thus eventually got devalued. there still is value so you should use them but dont worry too much because they are not as valuable as they used to be.