Perhaps a multiclass is the answer. Rogue/Bard might be appropriate.
Here's what I would do to try and create a character like this.
First off: play a Variant Human, and start with the Sharpshooter feat. This will give you that extra range and damage with the sling.
Begin as a Rogue, eventually choosing the Swashbuckler subclass from Xanathar's Guide to Everything. Take Expertise in Acrobatics and Persuasion at level 1, and in Stealth and another ability of your choice at level 6. This will give you excellent acrobatics, stealth, and persuasion. At level 4, take the Resilient feat, choosing to give yourself Proficiency in Wisdom saves, increasing your resistance to most Charm effects. Your sling and swordsmanship abilities will be represented by the ever-increasing damage of your Sneak Attack. Melee Sneak Attacks are made more easily thanks to the Swashbuckler level 3 ability Rakish Audacity, which lets you Sneak Attack if your target is the only creature (ally or enemy) within 5 feet of you. A Rapier will probably be your melee weapon of choice.
There is some room for flexibility, but you will probably want to end up with at least 13 levels in Rogue to gain the Swashbuckler ability Elegant Maneuver. This allows you to use a Bonus Action on your turn to gain advantage on the next Acrobatics check you make during the same turn. This will raise your already Expertised Acrobatics ability even higher.
To improve your swordsmanship and grant some Arcane spellcasting, I would also take several levels of Bard. By taking 6 levels of Bard and choosing the College of Swords (also from Xanathar's Guide to Everything), you can gain several benefits for this build. At level 3, you gain the Dueling fighting style, to further enhance your swordsmanship. You also gain the Blade Flourish ability, which allows you to use Bardic Inspiration to improve your attacks and can be used to represent your superior swordsmanship when combined with acrobatic skill. At level 6, you gain the Extra Attack feature, which will improve your melee capabilities even further. You also gain the ability Countercharm which allows you to use our Action to gain advantage on saving throws against Charm or Fear until the end of your next turn. This (on top of the Resilient feat mentioned earlier) fits in with being "fairly resistant" to Charm effects. From 6 Bard levels, you will also gain access to Illusion spells up to third level. You have the option to choose other spells as well, but if you want to focus on Illusions, that's your prerogative.
Your bodysuit could take the form of the Rare magic item Glamoured studded leather. This is +1 studded leather armor that can change its appearance when you use a command word. If that's not stealthy enough for you, it could be paired with the uncommon Cloak of Elvenkind which gives advantage on Stealth checks. A rare Cloak of Displacement, which gives disadvantage to incoming attacks might also be a viable option. All of these are in the DMG.
In the end, you're probably going to end up with a level 13 Rogue/level 7 Bard or level 14 Rogue/level 6 Bard. I would recommend the latter as it gives the useful Rogue ability Blindsense. The levels can be taken in any order that makes the most sense to you.
I believe this build covers most of your main and optional criteria.