8% is reasonable, not cheap (in the region of 6%) and not expensive (in the region of 12%) so I wouldn't be too worried about that.
% fee is the usual way for architects to charge for their services so there's nothing unusual there - you can check with the RIAI, there is no scale of fees so each architect's fee will differ, some will operate on fixed fee basis, but to be frank, fairly few, generally for a contract value of 300k 8% seems quite good - 10% would be more normal and I know several design based firms that would charge as much as 18%.
As for your budget - 1700/sq.m. is slim enough, generally I would advise clients that somewhere in the region of 2000 - 2500/sq.m. would finish a job well so unfortunately - it is not surprising that the heat pump cannot be afforded, perhaps you can save money elsewhere?
And lastly - in relation to charging for extra meetings, hiring an architect, or any professional buys their time...to an extent - there has to be a limit and when you are not charging per hour, in plain business terms - limits must be set.
In general I would allow for an initial meeting, a subsequent meeting with sketch proposals, a follow up meeting with a more final design, occasionally a further meeting just to wrap things up and then the next meeting would be post planning to discuss tender and construction issues.
During tender & construction there will probably be a few meetings to finalise materials and finishes and perhaps internal layouts and then site meetings every 2 weeks. I think it is reasonable to charge for meetings above this. In general I would suggest asking for drawings to be emailed to you, print them, discuss them yourselves, list ideas / changes you may have and then either email back, telephone or request a meeting knowing that there's something concrete to discuss.
the building process and most particularly designing your own home is stressful - what your architect should have done at the beginning was to outline to you the entire process, key dates by which decisions must be made, what can be changed easily and what can't and therefore requires thought early on and in general make the whole process clear to you - I believe most good architects will do this.
Percolation testing would always be an extra and not included in the basic % fee agreed.
Hope that helps let you know that you're probably not alone in thinking all of these things, but that on the surface everything seems to be progressing normally. Perhaps, and I don't mean to be rude, you have either been demanding too much of your architects time, stretching the budget a little - or else you have a grumpy architect who promised you too much.