I have been running a Cheddar models Puffin unit for about 6 years now and whilst found it relatively expensive to purchase has been great fun and a worthwhile investment. Sadly Cheddar are no longer trading so that route is closed.
I think a beginner would be interested in some general tips, in no particular order:
1) Steam is great fun but it's not like an electric motor it needs some sensible servicing and looking after.
2) It's duration on the water is strictly limited unless you get water feed pumps which increases the complexity and expense.
4) A Puffin unit will run for 30 mins non stop with a gentle fire.
5) Simple is best but a single acting Mamod unit or similar, wont self start and won't give you much power albeit it will chug along a small model for maybe 15 mins? You may also find the limitations of such a unit rapidly put you off, but they can still be fun but don't expect exciting performance.
6) Keep it simple and don't try to buy all the gizmo's out there until you have gained some practical experience of actually sailing steam. If your first installation is too complex you will get discouraged as one adjustment leads to another.
7) Steam is not hard but it is hot and it is different from electric.
By and large an electric motor will allways be significantly cheaper, have much more power and be easier to control than a steam engine, but, it's not as much fun!
9) Unfortunately to get a practical steam plant off the shelf that will perform like an electric motor will cost in the region of £400 - £700. By that I mean steam up, sail with proportional forward and reverse and a reasonable duration, say 30 mins, but it will last a lifetime and will continue to chug away long after the electric motor had expired.
10) Generally steam is not for fast boats - a gentle walking pace is about the best you will get, unless you start to get complex and expensive.
11) It is not hard to operate, you will probably gain practical knowledge in about 2-3 sails.
12) Don't be discouraged by the complexities - most of us drive but don't know how a car works in detail! Steam is the same, it's fine to just try it, but as per item 9) above, it's not cheap.
Hope this helps