Don't think negatively - once you get past this - and you will, you will have a NICE rebuilt boat and one in which you can enjoy YEARS of fun in! I do think that if you go slow and plan your work, that it would be a pretty simple rebuild; surely not as intensive as when I had to replace both the inside & outside tin skins, with rounded chine features at the garboard transition!
That brace between the flat part of the transom top and the corner looks to be reusable. The trim cap can easily be replaced by a piece of U-channel from https://www.grainger.com or other aluminum source.
For those corners, even if needed, pieces oversize by a good 1-1/2" to 2" (where one welded) could be fab'd from 5052 sheet alloy and could be made where they would bolt back onto the hull, where that extension folds down and is bolted to the transom or the topsides/gunnel on the other edge. I mean, just because it was welded in its original form, doesn't mean it needs to be welded at the corners on the rebuild. Now of course you can ... but it isn't mandatory.
And formed or cast aluminum corners, some with grab handles, can usually be found on eBay too. See the pictures of those I just found in a simple search for the terms "aluminum boat transom corner". Now $50 each might not be cheap ... but what is the cost of welding, if you can't do it yourself?
