Family lawyer here.
Some completely wrong advice being given.
International relocation: I know you are not intending to go abroad, but the PP who said if you did you'd face custodial sentence and lose "custody" (not called custody since the 1980s, it's called "residence") of the children, that is wrong. Theoretically it's a criminal offence but it wouldn't be pursued in this way - you'd be brought back pretty swiftly under the procedure/law set out in the Hague Convention on International Child Abduction - often you make it a condition of agreeing to come back (which you do if you have no defence, and the defences are extremely limited) that no criminal complaint will be made etc. In any residence case, the court would look at who is best placed to care for the children, you wouldn't automatically lose them for having gone.
Internal relocation (ie within the jurisdiction of England/Wales): theoretically he could stop you taking the children, not stop you going yourself (as a PP pointed out this effectively stops you going). If it ended up in court, it would look at what is in the children's best interests. have a look at these cases:
www.familylawweek.co.uk/site.aspx?i=ed153303
www.leavetoremove.info/latest-relocating-children/uk-relocation-not-abduction
The last one was where W just upped and went with no notice and H did not succeed in bringing the children back.
There is plenty of information if you google internal relocation.
If you are serious about this you need to try to avoid any sort of shared care arrangement, and to restrict H to alternate weekends and possibly a midweek (which is really the minimum these days) - he strengthens his position if there is a shared care arrangement.
Your solicitor should be able to advise you about this.
You'd need to have a good reason for wanting to relocate, and not just financial - eg some connection to that area, old friends, family etc who would provide a support network etc.
Maintenance: not sure how you've been advised you're entitled to 50% of his income. Maintenance is assessed on need. You could get more than 50% or less, there's no magic formula.
In fact, there is no magic formula at all, either for income or capital. The starting point after a marriage of any length is 50%, but need is a primary factor, and the welfare of the children, so you could justify a need for more than 50%, particular where H is a high earner and could get a mortgage. Every case turns on its unique facts, so don't be persuaded by a friend of a friend who says "well I got X" because there may be something about her case that made it very different from yours. Sometimes there is a "Mesher" order, which means that after the children are grown up and gone, you have to sell and repay a proportion to H so that you end up with 50:50 in the long run. Sometimes if W just gets a shade over 50% you wouldn't bother with a Mesher. Sometimes you can also choose to offset the pension entitlement, leaving H with his pension and taking more of the value of the home as a quid pro quo. There are lots of different options.
Maintenance and mortgages: in my experience (personal and professional) maintenance is counted as part of your income by mortgagees - I had to produce a copy of my court order in my last mortgage application and my maintenance was counted as income for the purposes of assessing how much they'd lend.