Since you are a new user, we highly recommend that you spend time going through the learning center and watching the videos listed here on the forum (Under Broadcasts) to get a good feel and knowledge for what the machine will do and find your own comfort level with doing simple things like cutting shapes out of lightweight card stock etc.
Multi cut is just a setting in the software - it defaults to "off" - but it has a drop down menu that allows 2-5 additional cuts. The settings don't change - it just repeats the "cut" as many times as you select. I feel that you really need to spend some time in the Learning Center and with the videos before you begin to tackle these materials.
The very best teacher is trial and error.... and the test cut button. There is a "guide" under FAQ in the learning center, but it is just that - a guide. Everyone sets their blades a little differently and material can vary. You will see people cutting regular vinyl anywhere from 2 - 40! It can also depend on which blade holder they are using which is a personal preference. For instance, I use the click blade for just about everything and love it. Many prefer the standard blade holder. There is no right or wrong - just what works best for you.
HTV can be one of the most difficult materials to cut. I suggest, once you are familiar with the machine and how it cuts, that you do some cutting with regular vinyl first before trying HTV. If you read the threads on the forum (you can search for topics) you will see a lot of tips and tricks, like putting glitter HTV face down on the mat for easier cutting.
I am not going to go into detail with the other questions right now. I think you have a lot of learning and experimenting to do and have not given a lot of info. Embossing or engraving metal depends on what kind of metal you are using. Also depends on the detail of the image - if you are engraving a hard metal you would use the engraving tip - if soft metal, you can emboss with the embossing tools. Additional videos with info are on
www.silverbulletcutters.comIf you are engraving you will want to hatchfill the design (discussed on here many times - there is now a setting in SCAL to do that) so you have a lot of detail. You can look in the Gallery on the forum to see different engraving projects that we have done. Engraving takes a long time, but the end result is worth it!
You just want a clean image no matter what you are doing. If it is node intensive, you may want to simplify the pattern and reduce the nodes. Remember each node is a message to the machine to move there - so the more nodes the more instructions to the machine.
I am not sure any of us can "suggest" a font as there are so many styles of fonts from printing to script to fancy to block - well you see what I mean. Not all fonts are clean and cut well. I would suggest you find one that you like and then use the pen tool to draw it and see if you like the end result so you are not wasting material.
Rhinestones are a detailed process using sticky flock for patterns. Some use SCAL for that, many use a rhinestone program and they have been talked about a lot here.
You are attempting to learn a lot about a lot. I would suggest that you take one thing at a time and get really adept at it before tackling another, or you could get really discouraged. There is a learning curve and it is why we suggest taking the time to do simple things on the machine and go through the learning center a few times before branching out. Those who have gone through the steps have been very successful.
I hope this helps a little. Take your time and you will have a great time creating!