Newbie tech questions

The first thing to do would be to visit the Phones & Technology section in the Travel Tips portion of this web site. It will give you a basic introduction to phones, SIM cards and using them in Europe. Then come back and ask more specific questions. In regard to which phone to use, chose the newest one but it has to be GSM capable and unlocked.

Will do...thank you Phillip!

Some people recommend the pre-teen down the street, but I find kids (including my 34 year old) are not patient with us slower learners and don't know how to instruct. Sure, they can fix stuff but you will never know what they did.
Geek or Wheels, however, will do training.
Just because you have them, doesn't mean you need to take them traveling.
I have a tablet and a smart phone I travel with, but to be honest, I never used the phone as a phone, didn't by a separate sim card, didn't run google maps, didn't get charged for data and roaming charges....but managed seven cities in Spain, trains, planes, buses all on my own over 3 weeks and didn't get lost.
Maybe wifi is all you need. Certainly all you need for your tablet.
Determine what you use these 3 things for at home, then what you think you need while on the road.
Remember, people survived on the road before wifi, cell phones and even inexpensive international calling. Email and text messaging (using What'sApp - which is free use globally) has gotten me along fine for the past 6 years from Spain, France, Istanbul, Tanzania, Uganda, South America....

If you are unfamiliar with any topic (literally any topic in the world), just Google it. You'll find lots of resources, online articles (including wiki how and wikipedia), and Youtube videos. You have a digital library right at your fingertips...just start with a Google search and all will be revealed soon enough. There's a Youtube video for just about everything, no matter how mundane (even boiling eggs).

Your iPhone can be used for WiFi. WiFi is available at most hotels and many cafes, museums, and other places you may go. Free, usually. If it costs you will know and can choose to pay or not right then - no bills later or anything.
Just have cellular data OFF (settings — cellular) and your iPhone without a plan will work as a WiFi device.
Of course, your LG phone will work on WiFi too, so I don’t know if you will want the iPhone.

To keep from getting charged more you can keep your phone on “airplane mode” - no calls or texts - and only turn airplane mode off when you have WiFi. Or just turn off “cellular data”. I don’t have your same phone so don’t know where the setting is but a quick google will help.
This lets calls through (you will pay for calls) but no data (web use etc, which adds up fast). You can use the web on WiFi for free but using cellular data costs. You can call your carrier to add a plan to make this cheaper. ATT has one for $40 with cheap calls and a set amount of data.
All that depends on how much you want to use the phone.

Battery - just the usual, have the screen go to sleep after a minute or two inactive, brightness low, minimal data use. Close all apps so they aren’t running using power in the background. And if you are concerned consider a portable charger. This is a small lipstick size thing that you charge at night and then during the day you can plug your phone into it and it will charge the phone. Anker power core mini is one I have, there are plenty.
I also have a larger one (pack of cards size) which will charge the phone 3+ times before you need to recharge the charger.

While I'm not familiar with the LG devises, I will say that your iPhone4 is obsolete and no longer supported by Apple and may (may...) not be allowed on a cellular network. That being said, it doesn't sound like you're interested in getting a pay-as-you-go SIM card for it anyway.

In order to avoid racking up roaming fees, place the devises in airplane mode as soon as you board your flight and leave them that way for the duration of the trip. You can then turn the WIFI on and off (but leave the phone in airplane mode) in order to connect to free WIFI.

As for battery charging, take the appropriate battery chargers and power adapters. Modern electronic are dual voltage so the 220v found abroad is just fine and you DON'T need a voltage converter. You might also want to look into a small emergency battery devise. Something the size of a lipstick case can hold enough juice to recharge a phone.

A word of caution - do NOT go to any web site where you must enter credentials (username/password) in order to access the content while on a free and unrestricted WIFI network. This goes for everything from email to banking/credit card sites. If you to use your devise for banking or email use while traveling, install and use a Virtual Private Network.

As for being a tech novice, check your local community center or community college for non-credit technology courses geared for novice/casual users of technology.

I found that if I turned off location services (GPS) under "Settings" on my phone, the battery did not drain as fast. If I'm spending hours inside a museum or on a long train ride, I don't need to know exactly where I am on a map. That way, I wasn't worried that the phone would be dead when I wanted to take a photo later in the day.

Do use whichever devices you plan to take with you, prior to your trip. Mine don't get used too much on a day-to-day basis at home, but I've just discovered that my batteries don't seem to be holding a charge as long as they used to, so I may need to replace them.

A word of caution - do NOT go to any web site where you must enter credentials (username/password) in order to access the content while on a free and unrestricted WIFI network. This goes for everything from email to banking/credit card sites. If you to use your devise for banking or email use while traveling, install and use a Virtual Private Network.

I use a Virtual Private Network (VPN) sometimes, but for most websites, it's not necessary anymore, because most sites use SSL (https) encryption. The VPN encrypts your traffic to make it unreadable over a WiFi network - but so does the SSL encryption. Ten years ago, far fewer websites used SSL so it was a much bigger risk then than now to use an open WiFi network.

And a VPN doesn't protect you again phishing attacks (where someone is trying to get you to enter a password to steal credentials).

All of the previous information is spot on.

I stopped taking my iPad two years ago. Less stuff. My phone 6 is large enough for my old eyes to see what I need.

I do buy the ATT international plan just as a safe guard against forgetting to switch to airplane mode in the mornings.....it's the age thing again.

I do take advantage of the hotels' free wifi. Rarely have I wanted to take time when visiting places (away from the hotel) to check for messages, texts, emails, etc.

Rarely make calls. Called my Dad on his birthday last year while in Germany. Cost was of no concern to me.

My phone is really my back up camera. Gotta get those "look at me" shots for my FB friends.

Keep it simple. Be realistic about how much phone time you "need". Hope this helps.