Steve,
Yes, you can enter with your wife and stay under Balikbayan Privilege for 1 year.
If you want to secure permanent resident status anytime during that year you can do so by paying P44k to the immigration lawyers who will secure all needed documentation and submit the application.

Alternatively, you could secure your 13a permanent residency visa from the Philippine Embassy. Visit their website for the forms and needed documentations. The total costs aren't easy to define simply because of the varying costs for medical evidence etc. The costs involved for Police Clearance Certificates and legalisation of other documents are not too great. Mine cost about £300 all told for Police Clearance, marriage certificate and proof of income. The majority of the costs go on the whole legalisation process.

The route I took was to secure all needed legalised documents and then submit the application after arrival in the Philippines. Lots of reasons why that worked better for me.
Well hopefully as I still didn't submit.
My documents remain valid for 6 months and now that we finally received my wife's NSO birth certificate (delivered just last night at 6pm by courier) we'll be going to the immigration office next week.

Worst case scenario for me if things don't work as planned is leave the country before expiry of my BB 1 year stay for a holiday and return with the wife under a second BB 1 year stay. Then give P44k to the immigration lawyer to secure all needed UK docs and submit the application all over again.

All in all the costs of relocating visa-wise are insignificant when taken against the total costs of actually moving yourselves and your belongings

Yes, most of the documentary support has a validity limit. You'd need to check the individual documents to know but generally 6 months.
BTW if you apply for Police Clearance more than once within 6 months they just issue a copy of what you had before and dated at the original request date. Means it could have very little remaining validity.

Hope it helps a little