Of course, we know that stimulants do pose a risk to the heart - while not significantly higher, there still is a risk from the increased blood pressure and heart rate. The question is then, can we counteract these risks by taking beta blockers along with stimulants, or let's say, anything that increases acetylcholine along with stimulants? (Huperzine A is a strong substance that increases acetylcholine levels, since acetylcholine slows down the heart rate). Would this work out?

I've read studies where beta blockers didn't enhance survivability and actually increased mortality in some cases, contradictory to what one would expect. Eating lots of fruits and vegetables lowers blood pressure and that has been found to decrease mortality. There may be other drugs such as ACE inhibitors that might help but you should be able to drop your blood pressure a fair amount with just dietary changes and light exercise. Of course, you should talk to your doctor either way.

Oftentimes though, exercise + diet isn't enough.

Right, but my understanding is the decrease in heart rate and blood pressure from these drugs does not seem to produce a corresponding decrease in mortality.

In comparison with other antihypertensive drugs, the effect of beta blockers is less than optimum, with a raised risk of stroke. Hence, we believe that beta blockers should not remain first choice in the treatment of primary hypertension and should not be used as reference drugs in future randomised controlled trials of hypertension. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstract&list_uids=16257341&query_hl=18&itool=pubmed_DocSum)

You should consider seeing a cardiologist and getting an assessment of your current cardiovascular health and guidance for how to improve it in the future.