3 liter starter help

[Jbrew]

Looking to make a strong dark beer. Decided on a vanilla porter with a target OG of 1.090. Bought a pack of imperial darkness.
I am not brewing a lower gravity beer prior to this one, so I’m planning a 3 liter starter using a 1 gallon glass jug. I have done starters before, but nothing anywhere near this big.
My questions are: I should probably do a step rather then 3 liters at once correct?
I have a 1 liter flask and stir plate. Should I do a 700ml starter then move to the 3 liter size? Once in the gallon jug, I will not be using the stir plate.
And any advice how long a starter like this may take to complete, and how long can I keep the starter before pitching so I can accurately plan my brew date?
Thank you all

 

[bailey mountain brewer]

Assuming a 5 gallon batch, one 3 litre starter should get you the cell count you need depending on the date of your pack, I believe imperial states 200 billion to start with? I would do one step 5 days before brewday, put it in the fridge on day 3 so you can decant the liquid off at the beginning of brewday.

 

[Jbrew]

Thank you for the reply. So just go with 3 Liters right out at the start? This will be for a 3.5 gallon batch. At a pitch rate of 1.0, I’ll need about 286 billion cells. Imperial yeast is 200 billion cells, however my pack of yeast is now a month and a half old. The brewers friend pitch calculator I’m using says that my yeast has 66% viability leaving me at 130 billion cells.
Thank you

 

[Dog House Brew]

I think 3l for a 3.5g batch is a lot. That yeast is only 45 days old. I think it is important to have active yeast at pitch. If I did 3 liters, I’d save a little of that for another brew. BMB gave you good advice.

 

[tracer bullet]

I think 3l for a 3.5g batch is a lot.

Agreed. I do think everything @Nate R said above is perfect advice, but 1.090 and 3.5 gallons for what's basically a double pack of yeast... I wouldn't bother with the starter.

 

[bailey mountain brewer]

Agree with both, for a 3.5 gallon batch I'd just skip the starter with an imperial pack.