I'm not a winemaker so can't help with the recipe specifics but I am a huge port fan and can provide a little color. First off, Port is always fortified with brandy. But in this case, brandy just means distilled alcohol from grapes.... nothing like the brandy you would buy for personal consumption. The distillate used in port production is more similar to a grain-neutral spirit so I'd fortify with grain alcohol or vodka (obviously adjusting for alcohol by volume).
The typical grapes used in port are touriga nacional, touriga francesa, tinta roriz (tempranillo), tinta cao, and tinta barroca. (Note: I've had some incredible 100% Touriga Nacional non-fortified dry wines as well, excellent stuff if you can get your hands on it!) I'm not sure the best way to replicate these types of grapes at home...
The must is fermented but the distilled alcohol is added after a few days to stop fermentation leaving the desired sugar concentration (hence the sweetness). I would guess the best way to do it at home is to measure gravity every few days until you're satisfied and then add the distilled alcohol. Aging takes place in wood for tawny port, stainless for ruby, or in the bottle for vintage.
Looks like your recipe is more of a farmhouse wine. No grapes. No fortification. I've had variations of port that are excellent. One had fruit. The other was made with zinfandel grapes from sonoma county.
Anyway, hopefully some home winemakers will chime in but I'd suggest scrapping the DME. Adding grapes or grape concentrate. Scrapping the sugar and acid blend. Fortifying with grain alcohol. And probably aging for at least a year (on oak if so desired). Just my 2 cents. Hope it helps!
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