Yes 5-MeO-DALT is serotonergic but so is 4-HO-MET and virtually all other psychedelics (not counting other drugs with partial psychedelic aspects), it is not a simple explanation for 5-MeO-DALTs side-effects. The long term damage Vader is talking about is disputable and not realistic because it pertains mostly to long-term exposure to compounds that have significant 5-HT2B activity I guess like mephedrone and flephedrone etc.
The problem with 5-MeO-DALT may be something like beta adrenergic activity, I am not sure. Also not sure if it is remedied by a beta blocker or if that is even smart... but you can expect more panic or anxiety attacks from it when combined with another psychedelic. The combination with 4-HO-MET does not seem additionally dangerous though psychosomatic effects like confusion, fear and distress can make your heartrate go up which is not something you'd want on top of 5-MeO-DALT activity.
What kind of heart problems are we talking about here? Due to malnutrition, that sounds like irreversible problems and not true damage. Are you prone to anxiety? Chest pains?
Also, have you tried either compound by itself? It is a little foolish to consider such a combination without knowing the separate compounds in and out. Especially if you worry about aspects of your setting like your health!
We're all trying to help, but we don't have the total and clear truth on anything you ask ready on a silver platter, Vader doesn't and I don't either. If an answer does not help you, just be more patient. And (senior) modship does not mean we always need to be able to help as much as you want. Especially if it's not the domain of expertise. Vader is not particularly an agent of PD and neither of us are with ADD. While this is not necessarily an advanced (ADD) question, extensive knowledge on 5-MeO-DALT pharmacology - if it is even known!! - is indeed proximate to the advanced area.