We're starting a new game at 5th level.  My character is a tabaxi that "survived a lightning strike as a kit, and has slowly been manifesting powers of the storm every since".  I *don't* want to play a spellcaster (just played a Sorcerer in previous campaign), but I'm not against a few lightning themed "tricks".  For example, I'm taking Magic Initiate (GM bonus feat at 1st) with booming blade and green *lightning* blade , and a noncombat familiar (GM's restriction).  I am/was planning "Swashbuckler 4 / Fighter 1", with rapier and shield, blade cantrip for bonus damage, and lots of mobility.  (And, ironically, half-plate, because even with 18 DEX, it's 1pt better on AC than studded leather and all my DEX bonus.)

But some discussions have made me recently also consider using a Whip (for OA control and maximizing Sneak Attack options), and even exchanging the Fighter dip for a Tempest Cleric dip (again "tricks", not intending to pursue anything past level 1).  And now I'm lost in a see of "what ifs"!  TWF? whip+shield? Dual Wielder (instead of +2 DEX) for whip+rapier TWF?

help!

[Cleric spells would be Guidance, Light (lightning sparks), and Sacred Flame (lightning "radiance") or Word of Radiance (lightning blast), plus Cure Wounds, Shield of Faith (lightning), Detect Magic (fuzzy tingles).]

Suggestion 1: keep it simple, just stick with your original idea.

Suggestion 2: pick the option that you can turn into the most interesting character quality, rather than evaluating what everything offers mechanically. I'm not saying you're ignoring that, I don't know the first thing about you, but for me that's often an easier decision to make than just looking at the numbers. The value of mechanically different options can be hard to compare, or the difference can be so minute as to not make a difference. Go with your gut, not your brain. That'll cut down on the analysis paralysis. 

pick the option that you can turn into the most interesting character quality

I second this.

If you start to feel let down by the mechanical aspects of your character, you can discuss it with your DM later. It would feel worse for your character concept to be constrained by your choices.

Just as an aside, rather than take both booming and green "lightning" blade, why not swap one out for Lightning Lure? Give yourself a little battlefield control. Also worth bearing in mind (unless things have changed) that the blade cantrips only have a 5ft reach regardless of the weapon used so you might want to keep a rapier and whip on hand.

I thought more about what y'all said, and talked with the GM.  I decided to abandon the Whip Master idea -- taking the character in too many directions.  (My problem is that I have too many ideas, not enough opportunity to play!  I can just picture the tabaxi stalking down the street with a curious wrapped leather "bracer", only to shake it loose and lash at opponents with a lightning-charged whip!)

I'm still torn between the vanilla fighter dip (Dueling style and Second Wind) or the tempest cleric dip (Guidance, Shield of Faith, DC 13 thunderous rebuke).  I think both are "good choices".  I think the cleric would be "cooler" and enhance the lightning background aspect; I think fighter would be the better combatant (+2 all the time, and no need to be so MAD).  [I also pondered not taking "DEX+2" at 5th, taking the fighter dip, but also taking Magic Initiate/Cleric.]

But the GM said we're going to start at 3rd level for a couple sessions, then jump to 5th.  I guess I'll see how I like the swashbuckler concept at all (and learn the GM's style), then make my decision!  (Love to hear any other suggestions or advice though!)

I'll second Lightning Lure instead of GFB. Then you can have a greater variety in combat cantrips, and have the "thunder and lightning" vibe going.