[2.2] Hybrid Slayer Huntsman with BM theorycrafting [SC]

Hybrid two-hand bow and melee, because I like variation in playstyles - I use mainly bow and then swap to two-hand melee against rares, uniques, bosses and their pack (I use constraining rules as if I was RPing). So Im not being that serious. However, I want to base the build on something that can do Merciless. While hybrids may not be optimal, are they with Ascendancy and Slayers, now viable?

Passive SKill Tree

Focus lies on life leech and atk speed for Blood Magic. The core idea is to trigger Onslaught often, crit often and be constantly life leeching.

Nearly 50% split between dex and str nodes. Getting Graceful Assault first, then turn 180 degrees for life, life leach, BM and Iron Grip. Afte that I go for Acrobatics and Phase Atrobatics for survieability, building up atk speed, life leech and life on the way there.

The Iron Grip boosts the bow quite well, but the 2hnd melee will need some boosts in +str gear or otherwise. The +life nodes makes up for the evasion compared to a pure dex build.

Am I missing something, or does the two-hand spech of a Slayer combined with Iron Grip making a hybrid viable?

Tree:

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https://www.pathofexile.com/passive-skill-tree/AAAABAQBAAHcAecE5AX5CLEMcA48ERoUdRXsFfAWvxiRGbQj0yW8Mn426DpSOrM7tj_8R35JD0z_TipW-ldUWK9br15FXzlhUmVNapNtbG6Xbydza3XQdf1313fjeWh7FH8rhG-E2YZghrSHKYqzjAuS85OolLiaapsmmy2ezaOKpTWnMKlusKuygLVIuR25fLyfvTa-p83q1ELWitct2GDbT93j37_gw-d06Gbo1uyw7g7ynPTm9WH3vvlj_7A=

Skills
I have no ideas for skills yet, but know I need to focus on psysical dmg for both bow and two-hand melee. I will have mostly dex early but then go full hybrid str/dex s I move to grab BM.


Gear
No ideas yet. Suggestions?


Concerns / Feedback needed

Im hoping that Headsman and Graceful Assault Onslaught chance is stacking. Is it?

Im a newbie and really need feedback on how well you think it will work. Will I do enough damge and have enough surviveability for Merciless? What good choices for skills do I have?

Is Blood Magic + atk speed + Onslaught doable as a combo? I supose I need to use low mana cost skills only, so I dont have to hold back on the attacks.

Going hybrid in str/dex forces me to get Iron Grip, which constrains the build to physical damage. Is Iron Grip necessary for a hybrid, do you think?

Is there a way to do a similar build without Iron Grip and focus on elemental damage with bow and melee skills, do you think?

Feedback aprpeciated, Im a noob, playing for fun but want to be able to reach a high level without failing in the building :)