600MB is definitely too much, especially if everything will be loaded all at once.
That. 
depends... if he makes a good 3d modeller in html and his assets are 600mb that is not bad...
website means anything... beginning with just a single card to a full fledged html game...
BINGO! I'm amazing game in mind. Working on story line. It would be really difficult for me to agree some game development company therefore, I'm considering option of developing something on own as pilot project.
But, I do not know what kind of developer I require as I don't have much knowledge with development.
What qualification and expertise would I require for filtering good modellor in HTML? What are other options apart from HTML?
Any pro's and con's on HTML you can throw light on?
personally i like html for games, but it is a lot harder to develop a good game in html than in a standalone app.
have a look at some html game engines: http://html5gameengine.com/
i didnt test them tough... i'm a little old school and tend to avoid frameworks.
you'll need a developer with excellent html/js skills - but this depends on the game i guess.
flash is also a possibility. i did some games with it about ten years ago. its way more easy to develop, but not as user friendly (just imho) and it lacks the coolness factor
What qualification and expertise would I require for filtering good modellor in HTML?
dont know what you mean... if you are looking for someone who designs you 3d models its the same for any tech (flash, standalone, html and so on) as the difference is only in the game engine itself and not within its assets