Gear wise, you seem to have good, mid-level quality gear. If you're pretty happy with it, I wouldn't sweat much that you need to get better. You do have a backup setup though, right? We all need a backup.
I'm a firm believer that the most important items in your setup are the batteries. Both for performance and safety. As
@DaveP said, most people on this forum follow Battery Mooch's advice. Choose batteries for a regulated mod based on the wattage setting you use. You weren't specific on which battery models that you use. That's important to know because their specifications can vary greatly by model.
Samsung makes prime quality batteries. The IJoy and Toshiba brands I imagine are re-wrapped brands; neither are on Mooch's recommended battery list above.
WATTAGE PER SINGLE BATTERY on REGULATED MOD:
(Total wattage doubles using 2 batteries; Triples using 3 batteries.)
Up to 45W:
Samsung 18650 30Q, 3000 mah 15 amp CDR
Sony 18650VTC6 3000mAh 15 amp CDR
Up to 60W:
LG 18650HG2 3000mah 20 amp CDR
LG 18650HE4 2500 mah 20 amp CDR
Samsung 18650-25R, 2500 mah 20 amp CDR
Sanyo UR18650NSX, 2500 mah 20 amp CDR
Sony 18650VTC5, 2600 mah 20 amp CDR
Sony 18650VTC4, 2100 mah 23 amp CDR
Up to 75W:
LG 18650 HD4 2100 mah 25 amp CDR
LG 18650 HD2 2000 mah 25 amp CDR
Samsung 18650-24S, 2500 mah 25 amp CDR
Sony 18650VTC5A, 2500 mah 25 amp CDR
Molicel 18650-P26A, 2600 mah 25 amp CDR
Up to 90W:
LG18650HB6 1500mah 30 amp CDR
LG18650HB2 1500mAh 30 amp CDR
LG18650HB4 1500mAh 30 amp CDR
Samsung 18650-20S 2000mah 30 amp CDR
The Nitecore i4 is a decent, entry level, basic charger. No bells or whistles. I had one at one time and it was a slow charger. I upgraded to an Xtar VP4 that has a better screen and faster charging. I'm happier with the Xtar.
I'm not familiar with either your battery device or your juice attachment. IMO, the juice attachment is more important than the mod. The tank and its coils are what ultimately make the flavor and the vapor and therefore your satisfaction with your vape. The battery device just supplies power to the tank. It's a major plus if the mod feels comfortable in your hand while using it.
Concerning your tank, I did look for a review on You Tube by one of my favorite reviewers. The machine threading left something to be desired, but otherwise no real cons.