Question Gardian with Staff viable ?

Hi guys !

I am new to this game and, without searching for an optimal build, I would like to avoid going into something which just cannot work. We are not going to play any hardcore league anytime soon.

I am playing with two friends whose characters are Witch and Ranger, and I decided to play a tank.

I would like to know if I can be tanky with a staff ?
When I look into the passive skill tree planner, I see the dealing critical strikes can grants Endurance Charges, and blocking with it can grants Power Charges.

It seems the Staves are the only way to block without a shield (or Dual Wielding, but then I would rather play Marauder), this is why I was thinking about using them. And with Endurance Charges it could lead to be quite tanky.

At the beggining, I thought about using a Shield a passives to improve it; but then I've noticed this would lead me to the Marauder / Duelist part of the passive tree. So, Role-Playing talking, I said myself "then you should have play a Marauder". So right now my passive tree is this :

https://www.pathofexile.com/passive-skill-tree/3.0.0/AAAABAUDABT2NI49D0NjQ8hPBGjya9lxTYY7ms-vbA==

and I was planning to spend my points this way now :
https://www.pathofexile.com/passive-skill-tree/3.0.0/AAAABAUDABT2LdI0jj0PPvFDyEouTwRVqVnzW6Bo8moBa9lyqXwOhjuTB5e0m1GfPqdVp6Wsqq9sr6e5Q7yaxPbJZ9WL

But there are some things I am not sure how it works :

- if I take a "Staff Critical Strike Chance (+30% Global Critical Strike Chance while wielding a Staff)" + "Counterweight (+60% Global Critical Strike Chance while wielding a Staff)", does that means I have 90% of chance to deal a Critical Strike with a Staff ?

- if so, does having 10% of change "per hit" to get an Endurance Charge enough to build tankyness ?

- how many Endurance Charge can I have by default ? Should I try to get every "+1 Maximum Endurance Charges" tree points ?

- is it worth it to go to "Blunt Trauma" and "Serpent Stance" ? Or "Disemboweling" ? Is taking "Blunt Trauma" and "Serpent Stance" better than taking "Counterweight" ?

After this, I guess I should focus on Auras as a Templar Guardian ? Is this a good way to go ?
https://www.pathofexile.com/passive-skill-tree/3.0.0/AAAABAUDAA18FPYXLxzcHRQdqiSwKPot0jSOPQ8-8UNjQ8hGcUouTwRVqVfJWfNmnmjyagFr2XFNcg9yqYCkgOCGO48aj0aSK5MHl7Saz5swm1GfPqUYpwinpayqr2yvp7QMuJO5Q7yaxPbJZ9WL4Yjquuvu-tL-SQ==

For the last Ascendant points, should I go for Unwavering Faith or Harmony of Purpose ?

I know this is a lot of (stupid ?) question, but I would be really grateful for your answers :-)