With regards to caffeine, everybody is different.
Some people drink lots of coffee, so they have built a tolerance to it over many years. These people could probably have a gram a day it wouldn't put them out of whack.
My way of dealing with caffeine is as follows:
don't have any caffeine (tea/coffee), recreationally. This means no tea/coffee, generally.
I only take caffeine in my pre-workout drink (I use Superpump 250, every other day, whihc already contains caff, though you can use your favourite pre-workout drink, which will almost certainly use caffeine as the main stimulant).
I believe that I end up taking about 150mg, every other day, in SuperPump 250.
When I start cutting, I switch to an ECA stack. This, I take about 6 times a week and ingest somewhere in the region of 200mg/day. This much caffeine really hits me hard, because I have not built up a tolerance to the stuff.
My ECA phase lasts for about 2 months, before I come off it. This allows my body to lose its tolerance towards caffeine, once the 2 month period is done.
In summary, you have to learn to listen to your body. Experiment.
Start low and bump up the dose if you are not getting a response. And make sure you go through an "off period" of cycling of the product (very important).
And above all, don't take caffeine recreationally - save it up for your workouts/exercise. This will allow you to keep doses nice and low (for the workouts). Same goes for Ephedrine.
My belief is that caff is the best stimulant on the market, but it isn't marketed heavily by supplement companies because it is so cheaply/readily available. Its easier to charge £40 for a small tub of Super Heat Matrix 4000 Blitz Thermogen Extreme...not so easy to charge the same for caffeine tablets, available from your local supermarket.
Caff = super powerful and cheap stimulant. Highly recommended before workouts and when cutting.