Lemme get ya started with this excellent thread from Unbongwah:
link.
Some major things you'll want to answer: how multiclassed do you want to be, what T5 do you want, and do you want to use a buckler or not?
Just for Swashbuckling + Feydark you really only need Bard 3. FvS 1+ is really nice for Divine Might and free Magical Training, and Fighter (usually 6) is really good for bonus feats and enhancements - if you're going Buckler route in particular it can be really helpful to have more feats and access to Stalwart's improved options if you want some cheap defenses. Fighter 6 is also really good if you can use a build that benefits from Kensei Core 3 (which gives +1 crit multiplier) so handaxe/light pick builds are pretty tied to this. If you plan on Warchanter investment (which is really solid) you'll want more Bard levels though, as your CC duration is tied to that.
Warchanter will give you incredibly reliable CC (Cha-max with Divine Might = high DC), but it's single-target unless you get to the T5. You're also mentioning just using GCS, which is extremely good AoE CC but will require some investment and falls off at endgame (you have to give up too much of everything else to have viable spellcasting DC's at like level 28+) but that's not really an issue for leveling.
Buckler or not changes a few things - without one, you start straight out with 10% Doublestrike, +6 damage, and you can grab Offhand Versatility for a bunch of extra damage and be done. That's pretty great, and frees your feats up a bunch. With a buckler, you kinda have to grab 3 Shield Mastery feats - but you get 3/6/10% Doublestrike, can twist LSM for another 7% DS in epics, access to Stalwart Defender stuff (like +20% HP), 10% Dodge and some cheap PRR, and you get an entire gearslot extra to throw cool things in; also might have to grab Improved Shield Bash to hit things with it.
On a Greater Color Spray build you really want Quicken Spell, Heighten Spell (take this at higher levels), Quick Draw (reduces time between casting and swinging), and ideally Spell Focus: Illusion (so you can twist Illusion Specialist). Add that to 3x SWF feats, Improved Critical, Precision, and QoL stuff like Extend Spell and you see why feats get tight and multiclassing looks so good
My immediate thoughts are probably Bard/Fighter with 1 FvS level. You'd have plenty of CC via GCS and likely Freezing Ice as a backup, and a few levels of Fighter = bonus feats which is really helpful. A lot of where you go from there depends on what you're interested in
What are you thinking? I'd be happy to build something a lot more detailed but there's a lot of possible routes to take so I'd like to get one that fits your needs/interests better