https://www.gov.uk/psv-operator-licence ... sv-licence is where you'll find the information.
You will need finances of £3500 for the first vehicle and £1500 for the second on a restricted licence. The VOSA page is incorrect when it mentions vehicles under 8 seats, it should red over 8 seats and under 17 seats.
The EU regulations state readily available funds, so an overdraft facility, credit cards, cash in the bank will do. The TC will probably call you for a Public Inquiry as he tends to do with a lot of restricted licence applicants because so many abuse the system.
The restricted licence if for those who run say 3 or 4 cars and want to add a minibus to the fleet, or who may have a full time job and want to run a minibus as a sideline. The TC will want to see evidence of income from the other job, or cash flow forecasts. You will need off-road premises to operate from; you will need to have the vehicle safety checked, usually every 6-8 weeks whether it is used or not; you will have to have a tacho fitted and use it (except for regular runs such as school contracts). You will have to comply with the drivers hours, remember that taxi/ph work is still "work" and "driving" for the purpose of the drivers hours regulations.
The vehicle must have a Certificate of Initial fitness, so check that carefully before you buy any old minibus which can be of any age, unlike taxi/ph cars! I regularly run buses that are well over 60 years old with no problems, but that is my speciality.
For maintenance, get a written contract with a local garage who can deal with the minibus and make them aware that EVERYTHING they find defective MUST be fixed! The vehicle will need an annual test at a VOSA approved test facility (look up VOSA ATF for a list of your local ones). Do not treat the annual test as a "let's see what it fails on". It will flag you up as a "red" operator on the VOSA records and you will be the focus of attention at any VOSA inspections!
Have a look through the RouteOne website, court report pages, there's always lots of cases before the TC regarding errant restricted operators. Don't be one of them!
edit to add that your driver(s) will need the PSV licence and the driver cpc card to drive the minibus. Vosa stop + no driver cpc or tacho= immediate prohibition + hefty fine for driver + operator.