I made Breton character to try out magic oriented gameplay.

Does wards and alteration spells like stoneflesh stack?
If i use light armor will wards and stoneflesh stack on top of that physical armor i have equipped?

Alteration school has perk called "Magic resistance". Is this a passive perk that works all the time?
Breton's natural magic resistance 25% + "magic resistance" perk 30% + Lord stone 25% = 80% magic resistance <--is this correct?

not sure about the alteration spell stack but im pretty sure they dont.but they do on armor
yes the perk is passive and yes that would be 80%

With the Mage Armor perk to level 3, you get triple the armor of any given armor spell, but ONLY if you're not wearing armor. If you're wearing any armor, any armor spell will stack with your worn armor, but the Mage Armor perk would be useless to you.

Also, yes, as said above, you would have a lot of magic resistance stacked up, using that build.

Thanks, so no need to use wards if i have high magic resistance and if light armor + stoneflesh stacks.

Lesser ward can render you completely immune to dragon breath, as it isn't calculated as one large damage burst, but a series of small damage amounts, similar to the flames spell. Magic resistance itself is capped at 85%, so you will take some damage, none with the ward.

You can use a alteration spell such as Stoneflesh and the Ward, from the restoration school, to have a higher armour value.

So if Stoneflesh gave you 60 armour and the ward gave you 20, while you had the ward up you would have a armour value of 80. However with the last Shield spell in the alteration school you get the maximum protection, which is 80% damage reduction. Unless you use mods, I recommend "better magic" It really does make using cloths and shield spells worth it. Also a wards cost nothing mod.