Hi James, and welcome!
I hope you have a separate budget to spend on acoustic treatment for the room so the £5K does not have to include that as well as audio gear. If you don't, you won't have much left to spend on the gear.
You don't say how many input channels you think you may need, or what ways of working you hope to cover. By this I mean, for example, do you aim to record bands playing all at once, or would you only record one or two performers at a time ("tracking")? Your studio experience to date will tell you how some bands can work this way and some can't.
Is the venue set up so you have a separate control room acoustically isolated from the recording space? You need to be able to listen to the performance on loudspeaker monitors so you can hear properly whether you have the right type of microphone set up in the right position for each instrument. One of the hardest instruments to record is a drum kit, as it needs a really good acoustic space, a set of good microphones, multiple pre-amps and a multi-channel interface.
My advice would be to take this in stages. You could start off by suggesting that bands track their drums and bass in a pro studio and then bring the tracks to you for adding all the other instruments. This minimizes the band's time in an expensive studio and allows you to gain experience of your own in tracking these other parts. In addition, it means you can spend your budget incrementally, only buying the mics and other gear needed for these additional parts until the business, the acoustic space and your expertise have built up enough to track the rhythm sections as well.
That said, I would not advise aiming to master the recordings yourself, at least not for quite a while. Mastering needs different gear from that used for recording, a different pair of ears from those of the recording engineer and a different set of skills. The thing to do would be to go and sit in at the mastering sessions of your mixes in a mastering house so you can see and hear where your mixes are making life easy for the ME and where the problems are. This will improve your recording techniques.
There are lots of mics and interfaces we could recommend for the tracking work, but we first need to know how much you aim to cover with your budget.