Old Enha player here, I played spellhance endgame and seriously for about 2 years, and Enha endgame for about the same, have bis gear on both and many items to tweak around with from fight to fight.
1. Spellhance have a enormous short range AoE (magma totem, fire nova with glyph, chain lightning when storm strike debuff is up) and is more rng heavy due to maestrom proccs ending up boosting much more dmg for you then normal enha, the storm strike debuff on target also can be very hard to master since spellhance attacks MUCH faster and rather random due to fast wep vs Enha's slow weps and how PPM works in general in this game, it can drain the stack very fast also considering how major this debuff is to your dmg spellhance requires split second reaction that involves 3 spells/abilities to drasticly change rotation/priority.
The usual arguement is "Enhancement better single target and more stable while Spellhance is huge aoe and rather chaotic, but truth is that both these speccs are very rng itself and spellhance can outperform single target too, with alot of luck it's downright ridiculous the plays you can make.
2. The bis for Enhancement, Specially Spellhancement has been a hot topic specially due to changes / fixes to
the class and new found knowledge comming into play and also, some itemization do better vs single target.
Personally I go for RS 25 HC boots, but you need the other items with hit rating otherwise ofc BPC 25 HC boots, hit cap is extremely important as Enhancement.
3. As I stated earlier many have different views on this matter.
What you do want though for spellhance specially is CTS and STS the reason is, both have same ICD and your talent AND spells will double dip with this trinket combo.
Cloak, Rings, Neck especially is best to change overtime to what suits you best at that stage of your gearing process.
What many like to do is go for RS25HC cloak, Gunship or Bloodqueen neck depending on your hit rating and get the hit and expertise from Ikfirus leather chest from Gunship.
Allready a wall of text here while trying to keep it short... Enhancement in a nutshell.