How Hard would 10 mans with only 7 people be?

Hey all, a few friends and I are attempting a challenge where we play in a "bubble" similar to HC, and we will be leveling toons then going through the content in phases. We won't be playing with outside players and running our raids on 10 man difficult with 7 people(2/2/3). For example, we won't step into Ulduar or any further raids until our raid group has full cleared Naxx , EOE, and OS. Assuming we keep our gear current to the tiers, how difficult will this challenge be? The reason I ask is I'm not quite sure on the raid tuning for this server. Thank you for any responses!

I guess you need to make sure you have the classes and specs within your group of 7 people to be able to defeat every boss in a 10 instance, some bosses require specific classes and abilities to defeat it. hope this helps!