Basically, you did one mistake: engage Patchwerk as your first encounter. Patchwerk is one of the few gear-checks in Naxxramas and is a pure dps- and healerrace. You cannot succeed this boss if a) your dps is to weak and b) your healers are to weak. I expect you to play in a casual guild meaning you are not SWP equipped and therefore do not yet meet the requirements for the Patchwerk-encounter.
As Ciderhelm postet I would recommend engaging Anub'Rekhan as one of the first bosses in Naxx. I myself am raidleader in a casual guild (raiding about 3 times a week) and most of our members were t5-equipped in TBC (sadly we started t6-content one week before 3.0.2). This equipment + some blue quest-/dungeonrewards and few crafted items was fairly enough to kill Anub'Rekhan first try. We cleared the arachnidquarter on our first raidevening (it does hardly request good equipment - most bosses are only about the right tactics and a little practice - a huge thanks to ciderhelm @ this point for the great tacticguides!). I also consider Noth and (especially) Heigan fairly easy encounters - assuming you know and understand the tactics (Heigan's tactic is as known from TBC: step out of the fire, except it's not fire but green acid).
And again thanks Ciderhelm for the great guides. Sadly enough most of the people in my guild do not speak/understand English fluently and therefore I cannot post your guides in my forum. Nevertheless I often refer to your tactics/tips for the encounters.