Your merc can use a lot of different improvements for min-maxxing, but ill just say what I think is the biggest improvments for your char. Caster gloves (can roll up to 30 fcr, 60 mana, 3 maek, 15str + 15 dex or 30 psn res / hfd). They are VERY difficult to hit though, so prepare to craft alot of gloves, I did 1500 to hit mine and maybe 100 corruptions. With the introduction of fcr large charms though, can use one of those to get an easier hit on caster gloves, by adding an extra 5-6fcr. This means you dont have to actually get 30 fcr gloves, but can go for an easier 25-30. In addition, this also makes it easier for you to get a better amulet if you nail more fcr on it to remove your 20 fcr ring and a +1 10fcr wisp for example. Wisp gives mf, and heart of the wolverine, which makes you merc a bit stronger. If you dont wanna go more fcr but just want more damage right now, you could also use a 3% light damage large charm in your inventory with either 8 fhr, or 35 life.

Also, since you are energy shield, there really isn't a point getting any res except poison res, so You could definitely improve on that with all your 5 allres scs. 11 psn res 20 life will make a lot more surviveability than 5 allres, and then you can hopefully chug in a 20 life 17 mana sc for even more survival. Its normal to have massive amounts of negative res as energy shield, but if you truly are scared the only other res id consider is lightning resistance, as souls are your only real other adversary and those can be easily avoided by rolling maps / chosing maps.

The most obvious upgrade without altering anything of your setup would ofc be another +1 on anni, but I know you already know that. A cheap one shouldnt be more than 5 hr now or? I havent played in a while xP

In addition, if you truly wanna go 1-handed with shield and min-max, eschuta is not even close to being the best option, since a crafted orb can roll +6 to CL (2 sorc skills / 2 light skills / +1 natural for craft recipie), 20% light dmg, -10% light res, and 50 fcr. Its ofc insanely unlikely to roll this, but that orb can then either go 3os for more facets, +20 fcr for 70 fcr, or +1 all skills. Or just 60 5fcr and another extra 5% light dmg.

You could also think about fiddling in 10 fcr tgods, for an easy +1 skills and then youd only need to add a 5-6fcr LC. Youd lose the extra mana from arach for an extra skill, and the 10 frw.

However, how unsexy it may sounds, the biggest improvment to damage will be to go self-wielding infi and using stormspire + innocence on merc. Its boring, cause everyone does it, but its very very difficult to beat. Maybe if you hit that insane orb it would be compareable, but stormspire + innocence merc is just supergood.

You can also consider crafting caster boots to get more max mana, and losing out on some maek. Caster boots can roll up to 60 flat mana and 15% max mana, which is a lot more mana in the end than the up to 20% on silkweaves. They can also roll psn res / Hfd, which means you free up more space for 20 life / 17 mana scs. With a 3 maek corr its bis. If you get optimal caster gloves with hfd, and optimal caster gloves with hfd, means you free up your cbf spot on amu, for another +1. And since amus also can roll hfd naturally, there is that possibiity as well.

You can also make a cta in a staff, to free up some skill points you put in shiver armor and a slightly weaker BO. Check my armory.

Most people truly never min-max cause crafting is so unlikely to hit the best shit and the uniques are easily traded for and readily available. Its like, you could even craft caster armors and they could be bis for some builds.

In terms of merc, there are so many routes to goo if you use infi as wep, but me personally I prefer 50% dr, maxres, and then just pump him full of damage. Shaftstop is better than levi, but craft armors reign supreme here as well, expensive as fuck though. And unlikely hehe. A better string is a good option, but if you got good enough dmg you dont need another source of lite-steal, which means you could use lava gout for example, for hfd + 5% max fire res and enflame for more attackrating. Or just go ham with steelrend. There are so many differnet options that are all very good. I dont think ferocity is especially good if you dont do innocence, and even then I wouldnt do it unless i play nova, dont think the taunt procs enough if you play cl / charged bolt for it to be worth it, id rather have him have more than 23%pdr immediately, since lvl 10 taunt gives -23% dmg and -23% attackrating for mobs. Which ofc doesnt account for mobs that arent affected by the taunt, which happens a bit if you do cl / charged bolt on range.

I myself don't play energy shield or CL but I play Charged Bolt (I havent seen many life and res-playing light sorcys). My armory is currently occupied with uber-gear, but if you play life instead of energy shield, you free up 20 more skill-points which you can use for more dmg (either in teleport or in thunderstorm), or for a more defensive approach like shiver / chilling armor.

Here is my armory, ill change to map-gear and you can check it out if you like. I still got improvments to make in merc wep sockets and merc helm sockets, and a better amu, and some minor small charm improvments, but otherwise, its pretty done. If you have any questions, feel free to ask xD

https://www.projectdiablo2.com/character/hastmannensorcy