I have a few questions:
Without suspension will it be a rough ride? Is it worth paying extra for
Are they comfortable from the get go or do they take a while to get used to?
Do they take more power to ride than a DF bike?
Are they really pain free for hundreds of miles?
Should I go for a larger back wheel or the same as the front two?
I'm considering drum brakes due to lower maintenance and weatherproofing, good idea?
The basic answer to all these questions is both yes and no, it all comes down to personal preference.
Front suspension is probably yes, but I do use the hardest elastomer in mine.
I also tend to run fattish tyres at lowish pressure which helps.
From the get go, legs will hurt, bum and back less so, hands and arms not at all. Once you get fit, then you will probably hurt less. My back improves with being on the trike but YMMV.
If you try and go at the same speed as DF bikes then trikes take more effort. If you take it easy then trikes with the right gears can take less effort as you have no minimum speed.
My main pain area is my feet in very hot/cold weather as they run hot/cold. Apart from that then only the usual muscle aches.
If you want pure speed then the bigger back wheel is faster. If you do long multiday tours then the smaller back wheel is better as you need less spares.
No idea as I've always used disk brakes. Hydraulic disks are better than mechanical disks if you only use one brae lever but are not as robust.
Any downsides to a Recumbent in general or a Trike specifically?
Downsides .............
It's harder to use pubic transport (trains & busses) with a recumbent and almost impossible with a trike. On ferries you are still charged the same as a bike so not a problem.
It's harder to filter in heavy/stationary traffic as you can see less with a lower head position. Plus the extra width of a trike makes it harder to filter anyway.
This is more than offset by drivers in general giving you more room. So unless you ride in a lot of stop/start traffic not really an issue.
It doesn't take much in the way of a wall/hedge/long grass to block the view to the side, but the view to the front is better as you're not looking down at the road.
It's harder to ride with a group of DF riders as you are slower uphill and/or faster down.
Which area are you based in. I'm sure some one based near you can give you a better understanding of what a trike is like.