IPA isn’t a mean product to use at all. As long as you’re not in a a non-ventilated basement or a very very small room, you’ll be fine. Worse that can happen is headaches and dizziness but you’d have to inhale fumes directly on top of an IPA bath for a certain amount of time for that. The purest the IPA, the better your parts will get cleaned.
PreForm will warn you that parts are directly on the build platform but you can override this warning and still print the part as-is. Keep in mind that the surface area in contact with the Build Platform is critical and should be at least 100mm2 (as per Formlabs’ advice), and you should always use the layer slider to see how you part will print in order to avoid islands and unsupported areas. What I do when printing complex parts directly on the BP is that I orient the part flat (as I want to print it), generate the supports and then remove all supports except the ones on the face that will be places on the BP… that was I still get the minima, cups and unsupported areas. I then remove the supports when I’m confident the part will print correctly… As said by @StevePeters this method of printing, while supported by Formlabs, isn’t for the beginner.
As for printing remotely, since the printer doesn’t know if the cartridge vent is open or even of the build platform is mounted, Formlabs made the choice of forcing you to be in front of the machine before printing, thus reducing the chances of failures (printing without the build platform would basically ruin most of the resin that is in the tank). This points has been addressed several times in this forum and Formlabs keeps to its decision.
Another thing to take into consideration especially since you’re coming from an FDM printer : Because you have mastered your FDM printer doesn’t mean you know how to 3D print, it just means you know how to FDM print. SLA is a totally different beast just like SLS or DMLS are too. Take care and read Formlabs’ guides carefully and don’t hesitate to ask questions here (the community is very helpfull and Formlabs staff is always here).
You don’t want to UV cure until it’s completely dry.
Have you read that from Formlabs ? I don’t remember having ever seen this advice. I personally just use pressured air for a few seconds per parts to get rid of the IPA on the surface of the part, but waiting 5 minutes will do the same thing. I don’t feel the need to wait a couple of hours especially since as per the TDS of the resin the absorption rate is negligible for IPA (<1% after 24 hours), and in the port-curing white paper there is no mention of a waiting time betwen washing and curing.