Give extract brewing a miss, for the effort involved you will be selling yourself short. What advance is extract brewing over a can kit? It's the same stuff. One of the problems with 100% malt extract beers is that they tend to be overly sweet, especially if you start adding any crystal/caramel malts.
Much better to mash 2 to 2.5 kg of grain with a mini brew in a bag technique and then add that back to a can kit or tin of liquid malt extract and mix it all up in the fermenter. With that amount of grain in the beer you can control the degree of sweetness or dryness in the beer - something you can't do with malt extract. If you want a drier beer then mash at an exageratedly low temp to compensate for the sweetness of the malt extract or can kit.
If you are not sure how much grain you can handle, divide the litre volume of your pot by 6 to get the number of kgs of grain you can use.
For an amber ale you could use this grain bill:
Melanoidin malt 50 grams
Dark crystal malt 150 grams
Amber malt 300 grams
Ale malt 2000 grams
And add it back to a can of Morgans Royal Oak Amber ale, for a bitter beer, or a can of Coopers amber liquid malt extract, or a Nut Brown Ale. Mash temperature would be determined by how sweet or dry a beer you want, and by the attenuation character of the yeast you want to use.
For 2 to 2.5 kg of grain you would boil the resulting wort for 60 minutes and add flavour hops at 30 minutes and some aroma hops very late.
Here's more details and some recipes:
https://absolutehomebrew.com.au/partial_mash_technique_and_recipes
For the effort involved with malt extract beers (boiling,cooling, preparing specialty grain) this type of technique will get you a vastly superior beer. So much so, I think malt extract brewing is a waste of time.
Pat