I am a bit concerned about the coloring as it seems in the photos that it doesnt cover that much, perhaps it should be diluted?
The items pictured are likely finished in either:
- a waterbased finish, which typically are completely clear (water-white) once dry; they will minimally affect the colouring of wood and do little to alter the colour of paints that they're applied over (other than the usual thing with varnish of slightly decreasing saturation if the surface finish is made more matt);
- a commercial two-part finish such as catalysed lacquer which can affect colour essentially the same as described above.
It's not clear if your intended finish is a waterbased one or oil-based varnish however; the terms poly/polyurethane/PU can be used as shorthand for both types.
If it is the former you know what to expect.
If it's an oil-based varnish however expect a slight but noticeable yellowing of the wood even if applied thinly; I do personally think it's not an unpleasant colour change unless the varnish is applied quite heavily but personal taste is a huge factor here, with some people absolutely hating this colouring in maple..... and of course it's not what you're after here based on the pictured blocks.
I have experience painting with acrylic on canvas and paper and varnishing or sealing wood but never painting acryl on wood then varnishing afterwards.
Painting on wood with your acrylics won't present you with any new challenges :-) Paint adheres very well to wood even without a primer (the first coat keying nicely as long as the wood is clean and freshly prepared). It should also apply well since typically maple is dense and fairly uniform, but do be aware that small patches of wood can be much more absorbent than others due to differences in grain.
If you've never used a waterbased poly previously and that's what you end up using I'd recommend a wide golden taklon brush for application. Try to apply in long, smooth strokes and don't overwork the finish once it's down on the surface. And I highly recommend practising on some scraps before committing to finishing your project pieces.