On the banjo question ....
Bugbear is right that I'd normally say build light, but this is apparently not so for banjos! Those in the know seem to like heavy. I think this is because the skin head is about as light as you can get, and so needs to be in a very stable support to work at its best.
What I'd look for in a "beginner" banjo is much what has been said above:
1. Don't worry too much about "tone". All banjos are pretty loud and make similar sounds. Most of the tone comes from playing technique. Once you're good enough to recognise that your banjo's tone is sub-optimum, you'll be good enough to justify trading it in for a better one.
2. The most important thing is that it should be properly set up. Cheap factory instruments tend to have the nut slots too shallow, which makes playing on the lower frets hard work and not properly in tune. They also have high "action" (the height of the strings above the frets at the 12th or higher frets). The neck needs to be straight (and a banjo neck is long and thin, so tempted to move around) and have exactly the right amount of curve pulled into it by the strings (this is known as "relief", if you hold down a string at, say, the 1st and 12th frets, there should a little space between it and the frets at the 6th fret; but only a very little). If these are all wrong, only a very competent player can make the instrument sound good, and they will be working hard to do so. A beginner needs these right, so that the playing can be concentrated on. The woodworking analogy might be cutting with a blunt saw.
3. The construction needs to be sound, so the neck is firmly attached and the rim doesn't flex excessively, and so that it can be adjusted as needed.
Most of the £150 banjos can be sorted out if enough time and effort are spent (though some are probably beyond hope), but how is the beginner to know which ones, and how to fix them?
Two options I think:
a. Find a good player and take her or him to the shop. Once you've bought with your eyes, get the good player to play every one of that model which is in the shop. One will be better to play than all the rest, buy that one. With luck the player will be able to say "This one only needs the nut slots taking down and a tweak to the truss rod, and I can do that for you". Beer will need to be supplied.
b. Buy a second hand banjo from a good player whom you trust, on the basis that they will have set it up properly. Bit of a leap of faith, but most of the good players I know are rather concerned that beginners shouldn't start on badly set up instruments.