I like the idea of something like this for building skills – manuals, bunny books, dirt jumps, pump tracks etc.
Something like the canyon stitched or rose bruce? Rose might win for us short people!
What do I need to know?

You need to know that you can practice manuals, bunny books hops, dirt jumps, pump tracks on your current bike – be it a HT or FS.

The thing about not buying a specific ‘skills’ bike is that you’ll be learning on the bike you use on the trails. These skills you want take time and practice to master and more time to then transfer these skills onto your trail bike (i’ve found some suspension designs easier to manual and pump on than others for example). Better to learn on the bike you actually ride imo. If you get into jumping then id look at getting a DJ bike.

http://singletrackworld.com/forum/topic/jump-pump-track-bike

Completely agree with Euro

Whilst I agree you can practice skills/technique on any bike and it is good to get them nailed on your main bike it also depends a bit on what bikes the OP already has.

Pumptracks/DJs etc will be ridable but no fun on say a 29er full sus xc bike or a long travel enduro/dh bike so why not get a cheap little ht to play around on?

You can pick up a fun little hardtail for not much more the price of a pair of tyres off Pinkbike/ebay etc so why not?

If you can’t bunny hop or pump properly you’ll not be hitting proper dirt jumps anyway James. OP must/might be talking about little dirt doubles? In which case it makes no odds what bike you’re on. I’ve a 29er FS bike that flies round pump tracks. I admit it’s a little cumbersome in the tighter corners but not cumbersome enough to warrant a specific bike 😀

Dirt jumps are horrid on my fs 120mm 29er. Much better on my 27.5 150mm bike, but it allways feels like the wrong tool for the job.
A fun ht should be better & easier to practice the other skills on? I guess there’s always the need to transfer that to the trail bike.

Dirt jumps are horrid on my fs 120mm 29er. Much better on my 27.5 150mm bike, but it allways feels like the wrong tool for the job

Depends on the setup of the dirt jumps. Most you can ride on anything it’s true, but it’s much more fun on a BMX or short travel hardtail than on a full sus. Full sus does ‘hide’ some bad technique as well such as poor landings which lose you less speed on a full sus than on a BMX lets say. The steeper the transitions the more fun a short travel hardtail or BMX becomes. Basically theres nothing wrong with riding what you’ve got now or wanting to buy a cheaper, simpler bike to mess about on either. Depending on what’s available to you to ride I’d either look for a trail BMX, or a short travel (100mm max) hardtail with horizontal dropouts for singlespeed and one rear brake.
I have a little singlespeed hardtail with 24″ wheels that I use down at the track, but I choose to use a 26″ normal MTB (a stanton slackline) at some jumps I’ve built because they’re super fast and the ground isn’t that smooth.

If you don’t want a cheap cro-mo BMX what about a 24″ DMR jump bike they can be had cheap.