Hi Chris and welcome to the Forum.
Your offer seems reasonable and creditors will get their money much quicker. While the dividend may decrease this should be more than compensated by the shortened time period. Good luck and hopefully it will be accepted.
You can increase an offer at a variation but it would be better to make your best offer at the time. Your IP will want confirmation that the funds are available before calling the meeting so offer the £6,000 and best of luck.