Lycra cycling shorts VS cycling liners(cycling underwear) VS unpadded cycling tights
How do they compare to each other?
What are the Pros and Cons of each?

I have one pair of padded underwear that I wore once. Talk about getting you panties in a wad.
Sucked.

I don't care for "padded". I do care for a moisture absorbing chamois layer.
No sweat running down butt crack.

I have all of the above. If I'm in warm enough weather to sweat, I always wear cycling shorts and jersey for commuting, touring, or club rides. I have a padded liner that I'll combine with commuter pants on cold commute days or with tights on really cold commute days or long rides in cold weather. The combination of padded liners with commuter pants or tights feels bulkier than just padded shorts so I prefer shorts and jersey when the weather allows.

I prefer lightweight liner shorts that I wear under my touring shorts. I've tried plain compression shorts, that I use at home for rides less than two hours, but I had some chafing.

Racing kit is not compatible with my style of touring

Why seek 2nd hand Opinions?Buy 1 of each and Find out ..

there are little difference in cost of Bike shorts and the Liner things since the sales volume of cheap bike shorts is probably Greater .

Modest about Budgie smuggling? you can always wear cargo shorts over the Bike shorts.

Or Rain gear ..

My preferred option is to put the "chamois" in existing clothes. I use shorts or sweat pants and just sew in the peanut of fleece. Chamois is not my idea of practical on the touring trail. Fleece works well enough, and is easy to wash. Of course if you want to wear cycling specific weird wear, then there is no point in making your own. The advantage to making your own is either to save money, or look, non-idiotic, which is subjective.

Functionally a sewn in pad, without undies means no chaffing from the leg band of undies, or no double elastics at the waist, no double layers except where the fleece is inserted. Much more comfortable for riding. There are reasons why the clothes we normally wear have the form they do, they are clearly not as apt for a situation where you spend most of the day riding.

By the way, there is that ridiculous cotton death fabric thread. Most of the concerns about cotton shirts are a lot less real than similar concerns about cotton undies, if those would otherwise float your boat.

I was thinking I might beable to get away with tese wiggle.com.au | dhb Vaeon Roubaix Unpadded Waist Tight | Cycle Tights with no underwear underneath and running shorts over the top.

Also does hot or cold weather make it more necessary to have a pad/chamois?

Get some and try them.

Try them on longer distances than 40 km. That distance won't tell you anything. Try them on the distances you plan to ride. You've got lots of time (a year) before you go on your trip. Lots of time to experiment.

Base layer is your bike Shorts add what ever the temperature makes desirable, Over that.

I like the liners, as I can just wear regular shorts. I don't look good in Lycra ��

I tried liners and don't like them. I don't find cycling comfortable with out padding, so for long distances (anything past going around the corner) I wear padded cycling shorts- whether Lycra or the goofy baggy mountain bike type. I have always felt that when I arrive on a bike, whoever sees the bike will expect to see a cyclist. Wearing cycling specific clothing means, yep that's my bike. So, I don't care necessarily about what other people think about how I look. Add a RUSH cycling jersey, and I just blend in. When in Canada, do like the Canadians. Sorry, that's just the way I feel!