Hi @KimmiJ,
Unfortunately, the Hevea benchtop panels maximum length is 2.4 metres, so you would have to have a join in the middle of the benchtop. This can be done with a Kaboodle Benchtops Join Kit, where the edges are glued and the joiners are routed into the underside of the benchtop, then tightened to pull the panels tight to each other.
You'll have to account for the location of the sink, as you can't have a join in that location. This may require you to have joins on either side of the sink or to move the sink so it sits firmly inside the benchtop.
When you have decided on the location of your sink, mark its location on the benchtop, then drill a hole through it with a drill bit that is large enough to accommodate a jigsaw blade. Then, carefully cut out the hole for your sink. Check out Cutting Out Benchtops For Sinks And Cooktops for some guidance.
Considering you've had good results with the Kaboodle Clear Hardwax Oil, it would be best to follow on from what you did before. Make sure you give the whole surface a sand, then wipe it down to remove sawdust before applying 2-3 coats of your hard wax oil. Make sure you get all edges, including those inside the cutout for the sink. Check out Applying Clear Hard Wax Oil To Benchtops for some guidance.
Once the sink has been installed by your plumber, you'll have to seal it to the benchtop with a clear silicone like this Parfix Clear Bathroom And Kitchen Silicone. Check out How To Silicone a Gap for some guidance on this part of the process.
Let me know if you have any further questions.
Jacob
