@protean2213 Hey, hope I can help clarify.
T3 is a very well balanced set as far as stats go. It has high primary stats and a very strong mix of +heal and MP5. There is no wasted item budget on Spirit, resists or other less than ideal stats for our class/role. This stat balances makes it very attractive from a HEP value perspective. While not being the highest piece in any slot as far as +healing goes, many of the T3 pieces win out through HEP due to the high Int and MP5 values. These calculations also do not take into account Stamina which, in Classic PvE and in PvE in general throughout WoW, has been a critically undervalued stat outside tanking. I have recently updated my Naxx BiS list to include my current evaluations of gear available in Phase 6.
To your question(s). T3 is not the highest throughput set in that it doesn't have the highest available +healing. If you value only +healing then you can rely on the BiS items outlined in the AQ list or in the Highest +Heal w/ T2 3pc that I have just included after the Naxx gear list. If you value a balance of stats then T3 outcompetes many pieces in terms of overall value. This segues into the set bonuses. Let's work backwards from 8 to 2pc. The 8pc is fantastic, so fantastic Blizzard split it off into its own spell, Water Shield, in TBC. However, you can never equip it as you would lose T2 3pc. The 6pc is so situational it's just bad. The amount of thinking a player would have to do to have it meaningfully up at any given point in time is one both extremely high and would reduce the niche value of a well geared Shaman. Almost completely useless as far as I am concerned. From there the 4 and 2 pieces are good. If you have noticed a theme the set bonuses trend toward mana conservation. T3 2pc may have the highest use in Classic as the impact from a speed running view is high but the value from the MST would be negligible. Replacing totems frequently reduces the value of MST and therefore the 4pc. However, the average player will likely see some value out of 4pc. In all, T3 2pc and 8pc are the strongest set bonuses. If you subscribe to my evaluation of gear in Naxx while not running T2.5 5pc you will be using 5 pieces of T3 which will allow you to comfortably use the 2 and 4 piece bonuses.
@hifi369 You absolutely can. The spec lines out the generalist option but if you ever want to hard commit to deeper talents within a tree simply abandon Imp Healing Wave and Healing Way and commit yourself to CH and LHW as your throughput options.
The reason I like that spec and like having the "Deep Resto" talents is that, in case anything ever goes sideways or on progression where something unexpected occurs, you can switch roles and solidly tank heal. This is less true in Classic for some but equally as valuable as a player. I personally use the Healing Wave talents <1% of the time, however, when I needed it, it was there. If you want to specialize, no disagreement at all. Just know the cost of the trade.