What the army offers in terms of resettlement budget isn't going to deliver what you need, buddy.
You're simply not going to have the experience you need to get any sort of well paid work and you'll have way too much on your plate learning to be a civvi to even think about going self employed.
You need an outfit that will provide the training that the grant provides and then go on to be an employer that's sympathetic to the standard of training that's been provided.
I know a couple of people who took this up, seeing as you mention bricklaying. I don't think they do plastering.
Your unit resettlement officer (who usually knows f**k about all but that doesn't stop him advising) should have mentioned these people to you, but just in case he hasn't... The lads I know who did it were pretty happy with what they got and seemed to get into reasonably well paid work quite quickly.
Crucially, the employer knows exactly what standard you'll be at because they provided the training and so can provide continued support.