Regarding discounts just remember there is more to it than the headline price (which they will want to protect). You might be able to get something in terms of an allowance towards fixtures and fittings as they likely have a bit of markup on those anyway. So you can say look, you like the property, you are keen to move forward but act 'surprised' when you get the quotes for flooring etc (assuming you are considering it), maybe say that's more than you budgeted for so you need to look at funding for it, and see if they will offer a bit to seal the deal.
Admittedly, in the current market of rising prices there may be no shortage of buyers (they will tell you this regardless as their opening gambit, we had this even in the depths of the 2008 slump, even so far as saying "we don't send out brochures, we'd run out straight away") so you might not get very far, but just keep in mind their default stance will be a stonewall "no discounts, we don't need to give them the houses are flying off the shelves quicker than we can build them". That's just to set the tone for any negotiation, take it with a pinch of salt although as I say it's more plausible these days. At the end of the day, we ultimately bought our house for a price they said simply wasn't possible in the initial negotiations, admittedly in a different market than we see today.
Different builder btw.
Been a long time since I did this house malarkey 
