Looks like lot of potential ;)
If I might suggest, check local yards if you can buy ape wood.
This is high-density wood that is a bit heavier than fir, but several times stronger and having big moisture resistance.
When I was doing dryrot repairs on my camper, I used it for some critical blocking and add stainless steel brackets in lot of places.
Per my observation camper builders are using lumber coming from scraped pallets and staple them, so the only thing holding it well is siding.
I see your main overhang beam is having knot that takes probably 30% of its strength off -in critical point.
