You are welcome
Abbie and have to say that now that I have a rough idea of what you are working with as well the zone you are in - it certainly makes it a whole lot easier to come up with some suggestions.
There is however one question that immediately springs to mind on looking at your image and that is - are you wanting to leave the rock perimeter as it is - just rocks - or do you want to soften it and make it less like a boundary by planting it with plants that will compliment the rocks ?
As for the main area planting - my suggestion would be to keep the planting simple by choosing only a few different varieties and planting them in drifts or clumps - which can then be repeated throughout the area - rather than choosing lots of individually different plants - as the latter tends to look too busy and will detract from the focal point of the pond.
As your hibiscus trees will only be in bloom in late summer and will lose their leaves over the winter - I'm thinking that you are probably looking for plants that will give you year round color and texture and although there are many more than I can list here - here are a few suggestions of plants that are well worth considering as not only are they stunning to look at - but vary in height and include " walk on it " ground cover for between the stepping stones - all of which are perennial. low maintenance as well as many being evergreen and suitable for growing in your zone.
Foliage plants - most of which have stunning year round color
Leauthcothe Fontanesiana Rainbow - evergreen needing slightly acidic soil
Hostas - evergreen - all shades of blue and green as well as variagated
Houttuynia Cordata - Chameleon Plant - evergreen - spreads easily but in some areas can be invasive
Athyrium Niponicum - Japanese Painted Fern
Heuchera - Coral Bells - evergreen with hundreds of foliage colors to choose from
Hakonechloa Macra - semi - evergreen beautiful mounding grass that looks stunning near ponds
Ophiopogon Planiscapus - Black Mondo Grass - semi-evergreen - grass like but not an actual grass
Liriope Muscari - evergreen
Flowering Plants
Epimedium - Fairy Wings - evergreen with stunning foliage plus flowers
Hemerocallis - Daylilies - hardy and very adaptable to any conditions
Iris
Dianthus
Hellebores - evergreen
Veronicas - most varieties including ground cover
Persicaria Microcephala
Lewisia Cotyledon
Penstemon Barbatus
Geum Chiloense - evergreen
Laurentia Fluviatillis - Blue Star Creeper - " walk on it " ground cover
Sisyrinchium - evergreen with star shaped blue, yellow or cream flowers
I haven't included pictures as it would make this post even longer than it currently is - but have a browse through the list and see what may or may not appeal and should you require further information or even further suggestions - will be more than happy to oblige