Percolation tests are needed and worthwhile so get them done. After that - it depends on how much money you want to spend.
Generally I would advise engaging an engineer to do site suitability tests such a trial holes to see what kind of foundations will be required.
If the ground is suitable for percolation (septic tank) and for normal foundations then it should be fine.
However you can never fully tell what condition the ground is in without a Geotechnical Survey - this is very expensive though - most people just go for trial holes and percolation testing.
After that get a good architect to see if what you want will fit on the site.
Planning is always an issue though - just because there are other one-off houses in the area doesn't mean that they didn't sweat blood to get the permission or that your site will follow suit.
A few things to think about regarding the planning issue - is the site near any area of special amenity, or in a conservation area or heritage area - has the area been zoned for anything in particular - all this may be checked out in the Council's Development Plan and Development Plan Maps - have a look at them first, then percolation, then engineer & architect.
Good luck