Focusrite makes solid interfaces. They are good for the price. At the very least both of those are great for testing out GP on both Mac and Windows.
The RME is a big step up from a 2i2, but only if you use all the features unique to it. If not, you will be paying five times as much for a quality difference that you might not even notice on a live stage. You had mentioned durability, low latency, and reliability as concerns. All of those is where the Babyface Pro FS shines, but possibly not enough to justify the expense of getting one if the 2i2 will do what you need to do.
At the end of the day, the only correct answer to ‘what is the best thing for me to get’ is what works best for you. I’ll put a pros and cons of the Babyface Pro FS on the bottom if you are interested; there was a reason I mentioned it for your use case, but I highly recommend trying out GP with what you have before you put down money on anything else.
As for a DI box, I sort of went on a rant about that recently. The Focusrites and other quality audio interfaces output balanced line level signals which is all a FOH should need. If your goal is to prevent ground loops and to protect your gear from accidental +48v phantom power or gear that is not properly grounded, you would want an iso (isolation) box. DI boxes are meant to convert high impedance instrument level signals to low impedance line level signals. You don’t want to potentially alter your already fine balanced line level signal by plugging it into something that is expecting a different type of signal and converting it to something that could potentially wildly (or subtlety) effect gain, tone, or add distortion if all you want is isolation and a ground lift. An iso box maintains the impedance of a line level signal and passes it through while providing protection from rogue electrical anomalies from FOH and provides a ground lift.
As for VST plugins. Find what you like and works best for you. A few things to keep in mind: Not all VSTs are created equal - VSTs can vary wildly in CPU usage, RAM usage, and stability. Just because GP is a stable platform does not mean a poorly written or buggy VST won’t crash your system. Usually it is good to not mix VST types, and AU for Mac. It is common best practice to make sure you are using either VST(2), VST3, or AU (for Mac) and not mix types together. GP does let you disable plugins you are not using, and if a plugin installs more than one type you can disable the type you are not using. I’ve also found it might not be best to mix a bunch of plugins from different companies, especially on the same signal chain. Consider using a comprehensive modeler, or get effects plugins from the same source for a more reliable, consistent, and stable experience. Pay attention to the CPU usage when you turn on a plugin.
Also, a lesson I re-learned the hard way over the summer, 44.1Khz is just fine for live performance. If a VST is designed for 44.1 and has to up convert, that can eat unnecessary CPU cycles and RAM, sometimes by a lot and introduce instability.
As you are testing out GP with your gear and plugins, find a tone that you like, but also stress test and field test for stability. Don’t find settings you like and gig with it the next day. As with anything there is a learning curve - be ready to remake and streamline your rackspaces as you get better at GP. There are many different ways of doing the same thing in GP, some are more efficient than others.
Sounds like you have a good setup already, and I hope you enjoy the discovery process as you transition from amps to VSTs for live performance!
Babyface Pro FS - Pros and Cons
Pros:
Durability - It is made from a single block of machined aluminum. The bottom has a 3/8" for mounting which is nice for on stage.
Stability/Low Latency - RME creates their own USB drivers which are known for being ultra stable and low latency.
Reliability / Longevity - RME is still supporting all devices they have made since 2001. They don’t abandon their hardware. There is no planned end of life like some companies.
Class Compliant Mode - the Babyface Pro FS can actually be used as a stand alone mixer, as well as hook up to tablets and phone in class compliant mode (which you have to switch to).
(For a guitarist specifically) Two high quality XLR mic preamps (if you sing as well) with individual switchable phantom power, plus two high quality instrument level inputs. You do not need a DI box to plug a guitar directly into the Babyface Pro FS. With two instrument level inputs you could have two guitars hooked up at the same time, each going to its own effects chain.
Quality Professional line level XLR outputs - there is a switch on the bottom of the unit to go from +4 to -10. Very clean and lots of headroom, very low noise floor.
Two headphone jacks, one quarter inch and one 1/8" and handles both high impedance and low impedance headphones very well.
Optical ADAT or SPDIF for adding more preamps and outputs. Besides inputs, after sending a stereo signal to FOH, imagine running your signal(s) to onstage FRFR (or two), IEMs, each with their own mix. With an ADAT preamp you get 12 inputs and 12 outputs at the same time.
MIDI I/O - add a MIDI pedalboard to control your VSTs and/or GP.
Case - A nice touch for gigging, it comes in a nice case with places for USB and MIDI breakout cables.
TotalmixFX - RMEs awesome mixing software built into the unit itself. 3 band EQ per channel, plus reverb and echo. Very powerful and useful. Built in effects are stable and reduce CPU usage. It also can be controlled by MIDI or OSC.
CONS:
TotalmixFX - The software is designed with a non-standard workflow in mind. Many people don’t get it or like the learning curve and get frustrated with it. You either have a TotalmixFX ‘A-ha!’ epiphany moment and think its the greatest thing ever, or you hate it. I have not seen many people in between. You CAN disable TotalmixFX and use your DAW for routing instead.
Cost - The Babayface Pro FS is about four to five times the cost of the 2i2. If none of the pros appeal to your use case, it might not be worth it to you.
Too Clean? - One (strange) criticism I sometimes hear is that the preamps are so clean and transparent that the sound sounds ‘sterile’.
No Android support for Totalmix Remote - TotalmixFX has a remote version for Windows, Mac, and iPad, but not Android or iPhone.
See our article here: 
), or with seeking community help in case of issues… PC users most probably won’t be able to use those files without losing the plugin configuration and parameter assignment.
. Are there other, more budget oriented recommandations?