With a click castsequence, you don't want these macro's on separate hotkeys.

You want a single hotkey for the master macro.
This master macro will have a lot of:
/Click MultiBarRightButton3
/Click MultiBarRightButton4
/Click MultiBarRightButton5

You can use:
/Click MultiBarBottomLeft
/Click MultiBarBottomRight
/Click MultiBarRight
/Click MultiBarLeft

And:
Button1 through Button12

You also need to know your personal spam speed.
Watch the clock or get a stopwatch and "spam" a key like 1 or X, for 15 or 30 seconds.
Pick a speed which is comfortable for you to maintain.
At least 2 presses a second and up to as many as you can comfortably maintain is your goal.

So take your first spell, the one which you want to have up always, and put it into your first spam macro.
I call this one DPS1 within the wow client.

A spell like say Agony can be recast every 1.5 seconds (or faster with talents/haste).
Spells like this, you want to insert comma's equal to the spells duration.
If your spell lasts 18 seconds and then expires, you need 18 seconds worth of spam comma's in the macro.
If you spam at 2 clicks per second, put in (2x18 = 36 - 1 = 35) 35 comma's.
If you spam at 5 clicks per second, put in (5x18 = 90 -1 = 89) 89 comma's.

Once you have the first spell done, pick the next spell.

The 2nd spell is the next most important.
If the 1st spell and 2nd spell are both not on the target, the first one will be applied initially and the 2nd one after that. The 2nd one gets applied before the 3rd.

Repeat for as many spells as you'd like to use.

If you have a spell with a recast delay, rather then a duration before it expires, add in as many comma's as the seconds of delay until you can recast.

The master macro, needs one click command per macro in your click sequence.
If you want Immolate, Conflagrate, Corruption, Chaos Bolt and Incinerate, then your initial spam macro will have 5 /click MultiBarWhateverButton# commands.
That is one per spell that you want to use.

If you want G1 to spam the 1 key, that's fine.
I will strongly recommend spamming G1 and not setting it to toggle at a speed.
Spamming gets you extra keys (G-keys) to use.
Activating a toggle gets your account banned for botting.

The point of these macro's is to be able to spam a single key, and based on macro construction have it reapply your spells as they expire or as they are off of cooldown.

If you put a macro on each G-Key or keybind, then you'd actually be better off with no castsequences but just the spell straight from the spell book. In this case, you have to time everything yourself, not have the macro do the timing based on your spam speed.