What size pellet bag to buy

OMG, Maui comes home in 1 month after we get back from overseas! So excited.
I am now looking at getting him pellet food so everything is ready when he gets home. Currently the breeder is feeding him Vetafarm pellets with some seed and fruits/veg. But having looked at the Vetafarm pellet ingredients it looks like junk (so much peanut base!).

I'm able to get Roudybush and Harrisons, and I'd like to have him accept different brands of pellet in case I can't get one brand when we need to restock.

I don't want to get a massive bag until I know he likes them and will take that pellet brand. I can get a small bag of Harrisons (~500g) and a 1kg bag of Roudybush. But those weights mean nothing to me!

Would one of each of those sizes be ok to start (I plan to mix the pellets together in his dish)? Or should I get a big bag?

Or should I get the pellets he's currently eating and have small bags of the Harrison's and Roudybush and slowly introduce those whilst reducing the current pellets?

I'd love advice before I click 'buy' and get some food posted out to me!

My personal opinion only - I wouldn’t change his diet immediately on moving into a new environment (too many changes at once could be overwhelming). So I would buy a bag of his current diet, and a small bag of each of the others. I would let him settle and continue the diet he is used to for the first couple of weeks and let him settle in to your home. Then I would start adding one of the other pellets to his existing diet and gradually reduce the amount of his “old” pellets and see if he starts eating the new ones. I personally wouldn’t add both at the same time, although others might suggest a different strategy. My suggestions are based only on my experiences changing diets of 5/6 of my birds, not on any scientific strategy .

I get the 1 gallon bag, but I empty it into a sealed container... so it doesn't get stale mushy or too dry.

I order bags that are 1-2 lb. and feed my birds a mix of this with their other food.

As recommended above I would not suddenly change his diet completely to something else....get the pellets and same food that the breeder is feeding him and wean him off of it onto other pellets of your choice. A chop diet with veggies and sprouts would also be excellent for him.

Conversions:
g (grams) x .001 = Kilograms

Our Double-Yellow Headed Amazon weights about 500g and on the lbs scale, he comes in about 1 lb.

Kilograms x 2.205 = pounds (lbs)
1 Kilogram x 2.205 = 2.205 lbs

Strong Recommendation, at first, buy small bags and place them into the Freezer for at least two weeks. This for all dry foods for your Parrot. Both Seed and Pellets. After two weeks (we freeze for a minimum of one month).
Break them down into one week servings and Freeze the balance in like sized packages. This will keep everything fresh regardless of the temperature of the home.
As stated above, do not change your Parrot off of what it is currently use too!!! The last thing you want is to starve your Parrot, as this common leads to behavioral problems.

With a new Parrot, we begin mixing in the new diet about a week after arrival. We take up to three to six months to transition to the new diet!!!

It is very important to include Fresh Green Veggies early-on!!!

Conversion to a new diet takes time and patience, at least two weeks and in some cases longer. I'd experiment with a single type until accepted or definitively rejected, then try another.

Harrison's is one of many excellent pellets. Their conversion protocol is excellent and ought work regardless of brand: https://www.harrisonsbirdfoods.com/using-our-foods/large-bird-conversion/

Thanks for the advice everyone, it’s exactly what I needed.
Māui is (thankfully) a pig and will eat anything if he sees me eat it first. I’ll pick up a big bag of what he’s eating now and a small bag of Harrisons and see how he likes it.

I’ve made sure that when he comes home he’ll be spending a week where I’m pottering around the house and going out for short periods occasionally, so he can get used to being on his own slowly (the second week both of us will be at work during the day).

He already has some fruits and veges at the breeders, and I’m planning to eventually give that as the morning meal and for foraging during the day and the pellets at night. But I’ll stick with how he’s fed currently (pellets morning and evening) first with the veges during the day as snacks around the cage while we’re at work (like currently), and wean him onto the new pellets gradually before I change him to the fresh in the morning/day foraging, and pellets at night. I will of course check this with the CAV (he has his first appointment the end of the first week he’s home).

I definitely don’t want to starve him, but do want him to not eat junk eventually either!

On the bag size, I buy the smallest bags I can, usually 1lb of Harrisons. This lasts Nike more than the six weeks that most brands say to use open pellets in. The 5 lb bag lasted her 6 months, the pellets looked good but I cant believe that they were still fresh and tasted the same as when first opened.

I'd rather spend more money for smaller bags and have it fresh till it's finished.