I've had some new forks which have slackened my head angle, I've also noticed that it's not quite as easy to steer.

If I changed to a 0 deg stem instead of 5 deg and shortened/lengthened my stem would it help?

yes it's a 'longer' lever

Is that yes to both?

I'd say that the stem angle isn't going to make that much of a difference as it won't actually change the head angle, just remove a bit of the height that the increased travel has put in there. The stem length will make a difference to the ease of steering, but a longer stem will also slow the steering down.

0 degree stem will help with steering as little more leverage, sorry typing one handed with crying puking baby on shoulder 🙂

The front wheel is coming up to meet me alot more on steep climbs, is that helped by a 0 deg stem?

Should do as it will lower your height over the front end.