My advice would be to join (subscribe) to the website
www.benefitsandwork.co.uk
It costs £20 a yr but is worth 10 times that in my experience.
They have a forum which is moderated by people who are trained to know about the different benefits, the advice there is top notch & has helped me massively.
If you were on ESA i could have said more but now that has been subsumed into UC i am very confused by it all.
Your concern about whether its possible if the tribunal decide against you for PIP they could look again at your UC. I'm afraid they
could, yes.
But it depends, being put in the Limited Capability for Work Related Activity Group is based on your having fulfilled certain specific criteria, & depending on
which criteria you were judged to make it into the LCWRA group under, will make the difference. Because the criteria are different. Edited to add: But if you get yourself clued up & preferably, get some help/support too, then you should in therory be able to use the UC assessors report to challenge the PIP one. Its a tricky situation i hope you can access some support. Do you have any lined up - eg Citizens Advice bureau? Perhaps your local
www.lawcentres.org.uk could help you? an appeal is a big deal to tackle alone.
How many points were you given for PIP in the Daily living & Mobility Categories? Have you got yourself a copy of the assessors report?
I am sure if you ask the question in the forum on B&W website, linked to above, & read their guides to both, & guide to appeals (a marathon in itself) you'll be better equipped. They are absolutely first rate.
Good luck with it, its a nightmare system i feel for you