[@Ryonara]The only item barring the estus flask that can restore your health in this is the Divine blessing, so no to the Rouge waters; also the more complex the item and expensive, the fewer you can have of them on your person at the beginning as well as how rare they will be found during the roleplay.
I had planned on giving my OOC a bit of a clean up, but I'm a bit pooped at the moment, I've typed a good 20 pages this evening on other projects and my CS for this.

So barring health restoration items, with the exception of Divine blessing most other items are in this roleplay - spell uses are restored at bonfires.
If your character is a pure mage, then typically I will allow them to use spells far more often than those whom are more combat focused but utilise spells to enhance themselves, so from what you're saying with you character I can see they are very reliant on spells; as such they will be able to cast them a lot prior to resting.
I'm not putting numbers on things because that pushes D&D territory, I'm leaving it to the discretion of the roleplayer and putting faith in them that they will use them responsibly.

In terms of parrying, it's a dangerous venture to do that if you're not a very dexterous character - unlike the games where dexterity has nothing to do with it.  
Dexterity is how swift one can be, the more dexterous one is the easier and more reliably they can parry - as a squishy assassin type character, parrying wouldn't be a recommended avenue of defense, unless of course you plan to have your character dexterous enough to be able to parry effectively.

Trust me when I say I loathe having numbers in this roleplay; I believe good roleplaying and utilising what you have based on the scenario given should define outcomes, not statistics - but in this element its more common sense, someone who is light and quick will be far more capable of parrying than those who rely on brute strength or magic to deal with their problems.

Technically any blade is capable of parrying, but the smaller and thinner ones are far more likely to be successful in doing so; so in answer to your question, yes you can.