Linux newbie - a few questions

I’ve recently installed Lubuntu on two laptops. One is quite low powered and the other only has slightly more grunt. I installed an SSD in one and installed Lubuntu without problems and am dual booting with Win 10.
Even thought I’ve installed a few distros int he past, I have a few questions as a relative newcomer:

If I want to try another distro from within Lubuntu and boot into a live USB and potentially install, how can I do that? I know how to do it from Win 10, but not Lubuntu.

Though I like the default Trojita email client, it’s not exactly what I want for work. Is there going to be any issue installing GTK based apps alongside QT ones or should I stick to QT applications instead? Does anyone have any other preferred email client?

Thanks,
Steve

If I want to try other systems, I’d download the ISOs, write to thumb-drive & boot them in ‘live’ mode (eg. the “Start Lubuntu” or “Try Ubuntu”) as it all runs in memory and doesn’t require installation or changes to your system. If you want to install; you could always use VirtualBox and virtual machines.

Yes you can use GTK+ programs happily on modern Lubuntu which is based on Qt. The only real negative is you’ll need both GTK+ (for programs) & Qt apps (for desktop) to be in memory; but if you’ve 4GB of RAM or more memory you won’t notice this in my opinion, even at 2GB of RAM it’s still okay, but you may notice a slightly slower performance when using memory hungry app(s).

I did (live) testing with 1GB ram machines for Lubuntu 18.10 & 19.04 and GTK+ apps still run, but the number of apps where performance drop isn’t noticeable does drop with the less ram.

Additional note: This doesn’t worry me, but if I load gnome-disks or many GNOME specific apps on my Lubuntu box; the top window dressing doesn’t perfectly match; eg. I like my CLOSE, MIN, MAX, SHADE (roll-up) on the top-left, but gnome-disks has it to the top-right looking different, without my beloved SHADE option available… This doesn’t impact all GTK+ apps, but for those that require a cosmetically perfect desktop, this may annoy them - I rarely notice

Thank you. Do you have a preferred email client?

So, I know how to boot onto a live distro from Windows. I just set it to boot a UEFI device. But how can I do that from within the Linux DE? Do I just insert the USB with the distro on it and it automatically recognises it?

One of my laptops only has Lubuntu on it, so how could I try another distro?

How you boot an OS on a box can be rather box specific. On most boxes I just press a Fn key and a menu appears that asks me if I want to boot a specific device and it boots. This includes recent dell desktops that aren’t mine and thus i cannot change anything (eg. dell inspiron 3258, 3470 etc).

A ‘live’ system means it boots as the only running OS so the key pressed is BIOS/UEFI dependent (and thus different for dells, hp, lenovo, sony including models from the same make).

I don’t know what you’re asking really which is why I mentioned VirtualBox (an easy way to run VMs). Your wording esp. within, makes me think you’re asking about VM options

The email client (MUA) I use is evolution (a gnome or GTK+ based client), and the reason I do is primarily because years ago (when using GNOME 2 or a decade ago) I found it easier to import my various email databases into it. I don’t usually change something unless i have as reason to so I have no idea if I’d choose it today sorry.

Thanks. I’ll try and explain. Coming from Windows if I want to use a Live distro from a USB, I just go into control panel and tell it to reboot with options for booting from a different siurce, or boot into the BIOS and change boot order. So how do I do that in Lubuntu? Do I put in the USB and reboot the system? Do I run terminal and put in some command? How do I change the boot order from within Lubuntu? I didn’t have a VM in mind. I am new to Linux, so I am very much used to a Windows world. Maybe if I put in a boot able USB and reboot Lubuntu, Grub will recognise it as a boot source and give me an option? I have no idea.

I’ve never done it from within windows, nor GNU/Linux (Lubuntu) either.

On any machine I use I just boot using the fn key (F12, F9, etc) or equiv. key (ESC, blue, black, thinkvantage etc) as specific for the machine. At worst it’ll mean I reboot the box maybe twice before I work out the key if the machine isn’t mine and thus I’m guessing keys. This is the only way I’ve done it (be it my own boxes with GNU/Linux on them, or borrowed machines usually with windows (7/10) on them.

I carry thumb-drives with me much of the time, so I can borrow ‘borrow’ a machine when I’m elsewhere, and I don’t need to touch or use their windows, only have them logout/reboot so I’m only using their keyboard, mouse, RAM & power but don’t go near any setting/hdd/ssd or their data.

Yes I could add a grub option to have it ask if I want to boot a thumb-drive, but I’ve never seen the need. I’d just reboot, and insert the thumb-drive as it’s in the late stages of rebooting and prior to POST (power-on-self-test). I then usually rapidly hit F9 if HP, F12 if dell or ESC for many pulls up a MENU asking what you want for loads of machines etc… You start pressing the appropriate key (or two keys alternating when I’m not sure which) as I recognize the box is about to finish it’s POST routines (and about to start loading OS).

My assumption here is x86 or x86_64 boxes only. I wouldn’t use this for different architectures.

Yes. I actually did hit f2, f9, f12, esc… All the usual suspects, but no BIOS. So, not sure if it’s something different here from Asus. I was just wondering if there was a specific command or option within the Linux DE to do it. Doesn’t seem like there is so I’ll experiment.