What are your top tips for building a fully off grid home on Southern Vancouver Island?

First off, THANK YOU for this site! Very grateful for your gracious sharing. My husband and I are embarking on a journey to build a fully off grid home in 2022 on Southern Vancouver Island. The lot is not serviceable by BC Hydro for any reasonbale cost (>$100,000) and in any event, off grid living has been a lifetime dream. We have finalized slab-on-grade and one story living over roughly 2,500 square feet to accomodate us + visitng kids and grandkids, etc. as we age. We have a large piece of land so no issues for space and placement. We are using many passive solar design principles: south facing windows in every room, limited north facing windows + concrete floors (+ radiant floor heating - (with a heat pump?)) for thermal mass + adequate eve overhang for summer sun protection. We will have solar PV + a back-up generator, since Vancouver Island weather will not offer sufficient solar radiation during winter. Our aim is to create a building envelop that accomplishes optimized energy efficiency. My question (s): Vancouver Island is much more temperate than say Quebec and Ontario, but we can still have a handful of days of -5 C. Can we or should we back off on R values of floor, walls, ceiling relative to colder climates? Is there a rule of thumb on this so we can know what good/better/best looks like for this climate? And finally, when it comes to sizing a heating (and potentially cooling) system (e.g., heat pump if we go that route), how do we ensure the passive solar heat gain we may benefit from is properly factored in? We feel like there are some things we will not know perfectly ahead of time when it comes to sizing.  Any other must know advice woud be greatly appreciated! Many thanks!