2Boxing - Warrior + (Enhc Shaman -OR- Priest) Discussion

Why am I going to play classic and my mentalityI have experience as Main tank in guilds, and the game felt too easy 40-mans private servers. so i want to spice it up by also becoming my own healer/support.

My gaming focus - Both PvP and PVE
I love PVP and BGs - going to spend alot of time in them. May not roll PVP server because im not a big fan of wPVP ganking
My play style will be Casual PVP /hardcore show up to all raids PVE,. I see raiding is mainly for better PVP gear, but also enjoy raiding,
but classic raiding is just too easy playing with 1 toon.

Already decided on warrior:
I will roll DPS warrior main, so i can MT and heal my own 5-mans. easy to find dps

Decisions decisions....
shadow priest -OR- Shaman Enhance / Resto

Discussion/ Questions:
Q1- Would shaman or priest be easier to play in 40-mans when im focusing on DPS with warrior?
Q2- Ench Shaman would be easier spec because they are both melee dps classes?
Q3 -Would shaman keep up with healing if I were to MT and Heal a 5-man?
Q4- Which dual box combo would be harder to play in PVP?
Q5- Solo pvp experience - is Enhanc or SPriest more fun to play SOLO in PVP? when im not 2boxing
Q6- Should I consider resto sham instead over enhance? Why?

p.s. I have cleared almost all raids in the entirety of WoW as MTank and priest alt, so don't get on my back about how it might be too hard dpsing warrior and also playing support in a 40-man.. i need a challenge so ill be dual boxing in raids in classic. And everyone knows most raids challenge are more gear-check and bad players, rather then actual boss functionality, (short of AQ40 and Naxx) - which I would just NOT dual-box those raids... duh.