Unless you are 145 or RJ type rated all new pilots start on the Dash 8 and more than likely at Manchester. There are no Dash 8s at BHX and no plans to base any there. There are 8s at SOU but being a popular base I'm not sure how often vacancies arrise there. Expect to be on the 8 for at least a year, possibly longer, although that may change (there are little or no command prospects in the company for the foreseeable future many jet FOs are trying their luck elsewhere).
Despite potential BA will not allow BACX to expand fleet so no prospects for promotion for a very long time if you are in the second half of the seniority list. Promotion at BACX is now almost always strictly on seniority. Again this might change.
Pay is average for Turboprops (mid to low 20ks initially)and workload is what you would expect for an airline these days. I can't answer what the roster mix is for the Dash 8 and how stable the rosters are. All I can tell you is what life is like at BHX on the RJ. The RJ rosters have stabilised of late but have been very heavy over the summer. Lots of max hour days follwed by minimum rest and lots of nightstops / tours. Unlikely to keep any standbys and generally work 5/2 with occassional 6/3 but there is no defined pattern.
Access to "BIG" BA. Over Big BALPA's dead body. Minor deal done recently but effectively have to apply to BA as an external candidate and until the very last minute you will be treated as such. Only advantage is a BACX person will be employed before any "similarly qualified" candidate. Read into that what you will. If you aren't Boeing Airbus which you won't be at BACX you are not equally qualified with most other candidates. Not saying I agree or disagree with position just stating the facts.
All in all BACX is not the Utopia of aviation but is a good place to start. It has a good reputation for standards and training which is important if you eventually wish to move on.
If you decide to go for it good luck.