Do those amounts sound right for a teeny lamb of 10" high? (Must weight him.) If he's still squitty do I assume he has a bacterial infection and get him to the vet? Anyone heard of giving them a probiotic?
The amount depends in part on the powder you are using; the ones I use are max 1L per lamb per day, others on here use ones that are max 1.5L per lamb per day. My rule of thumb is that from about a week old I expect any healthy orphan lamb to be consuming at least a half of the maximum per lamb per day - these are commercial lambs, that'll grow to 40-45kg liveweight in 3-4 months, smaller breeds would likely be less gutsy!
In the case of your recovering lamb, I think 100ml at a time of dilute formula is fine at this stage - again, please make sure that fresh water is available to him at all times. If he isn't scour-y tomorrow, you can start to increase the strength and size of the feeds over the next couple of days. From what you've said and done so far, it sounds to me like you have a good instinct for this - trust it.
Powdered colostrum contains probiotics (or at least, some do) - is that what you meant?
If he scours again, sorry to be a broken record, but I would get Rehydion and try that, as it is designed to be used with water or milk or anything in between, so you can make sure he's getting all his electrolytes and essential nutrients while gradually getting his system used to milk.
The trouble with starting with antibiotics is that they will kill off the gut bacteria that help him digest his food [question to VSS or jaykay or anyone else more knowledgeable than me on ruminant biology : is that right? they're not ruminant in the early stages - are gut bacteria still involved?]
Let us know how you get on - good luck