You are probably familiar with edge finding, indicating, setting offsets, and setting tools from your previous experience, so it really shouldn't be to hard to transfer to the Haas mill.
One thing on the Haas controls vs most other controls - being all buttons, don't get pushing too quickly. Make sure you push deliberately. It is a lot easier to accidentally push the wrong button then to turn the wrong nob (as on other controls) from my experience.
So, take your time - It is always better to be a little slower than to have to make another fixture, or part because of an incorrect button push.
Also - when you finally get a program you want to run - DRY RUN IT!!! Haas dry run is the stupidest thing ever invented and even Haas rep's say it is useless. So, don't use the dry run button ever (IMO).
INSTEAD:
Write down all your fixture offsets (and tools if you want to be really detailed) and then raise your fixture up a positive offset larger than your biggest -Z- negative move (so the tools are WELL above the part at their lowest Z.
(IOW - if your part is 2" thick and you are drilling through to say around 2.25", raise your Z offset 4" that way you are at least 1" above that part.)
Then run your program in 5% rapid with your hand always on the stop button. Watch for any moves that seem odd, double check everything, then lower your -Z- fixture offset back to where it was (you wrote it down, remember) and run your program. Keep the machine in 5% the first couple of times you run EACH program.
If you are only running one part, and don't have the probes, then simply set all your tools on top of the part, and your g54 offset will stay at ZERO. Then, when you are proving your program above the part you would just put like 4.0" positive in your g54 offset, run everything above, then put it back to zero.
Good luck - sounds like you will be fine