If I knew where you were posting from it would greatly help with advice.
Coopers and Muntons kit are usually for 23 litres, volume over flavor. The respective sites advise more flavor and body can be achieved with a volume of 19 litres.
The dry malt extract is probably in lieu of a kilo of sugar to increase ABV. The DME would add body and flavor. A kilo of sugar would give you higher ABV, but a thinner mouthfeel. Using DME to add body also requires the use of an 11 gram pack of premium yeast. The 5 to 7 gram pack of yeast included in the kit just will not give you a good fermentation.
The addition of the honey, in his experience, probably adds flavor and boosts the ABV.
This is a link to a ABV calculator.