The DIY approach can be fun and educational, but you might want to consider getting some pros in to at least see what they suggest.
The problem with WiFi on a commercial level is that it tends to be far more complicated than you think once you get to the point of needing more than one access point. It all depends on how big an area you need to cover, and how many users.
Boosters, plural, for example, may lead you into dark territory. It sounds simple: Access point > Booster (repeater) > Booster (repeater) and all's well, but in reality you usually lose 50% of the bandwidth at every hop, and on top of that you may have reliability issues, and ...well, it just isn't a good idea
Range to an access point is also an issue. Remember that as well as transmitting a signal, each access point has to receive it back from the phone/table/laptop, and these devices have tiny antennas. So, for example, having one huge omnidirectional antenna in the centre of the area with a radio running at the highest power legally allowed may seem like a good idea, it isn't usually. While it might be for some situations, in most cases you'll find that it really doesn't work very well and you'd be better of with multiple sector antennas and multiple radios, linked via 5Ghz if you can't use cables....and so on and so forth.
If you are likely to have more than about 30 people using the WiFi service at the same time per access point, you'll also encounter the "hidden node" issue, especially with omnidirectional antennas.
And on top of all that, there's also the legal side to consider. First of all, your broadband provider may not permit you to allow the public to share your connection. Secondly, although not (to my knowledge) currently required by law, you may want to consider some form of logging and even a signup system.
Imagine, if you will, that someone uses your connection for something bad. I mean really bad. So bad that the authorities get involved and break the door down at 3am. It is highly unlikely, but it could happen. It would be far better for you to be in a position to say "it wasn't me -- here are our logs and these are the user signups" rather than saying "err.. it wasn't me guv, honest".
And finally, you might want to use your wifi system as a free and unintrusive way to collect useful data about your visitors (e.g. email addresses/social media addresses) or something along those lines. That requires hotspot software/hardware.
These are all things to think about, anyway.
I don't know if I'm allowed to post multiple links in one post without it triggering anti-spam systems on the forum, so I'll just encourage you to search for things like:
Ubuquiti is an interesting WiFi hardware manufacturer. They have a number of options including a system called Unifi which is easy to manage and has outdoor and indoor units. Software running on a (dedicated) PC will help you manage the network and your users.
Netgear has a new range of WiFi access points that can connect together and be remotely managed AND it includes a Hotspot manager/login/ticket whatsit. There's a monthly charge per access point.
Zyxel has a number of "hospitality" wifi products including boxes that manage your hotspots, log access, manage users and even ticket printers. Basically youo can buy an all-in-one box that lets you manage everything from one place. Some of them are really, really good.
Microtik has a range of hardware that can do hotspot/gateway/various things.
Purplewifi is interesting and might be worth investigating. You should really look into this.I've not looked in detail but on the face of it it is very interesting.
Thecloud wifi is something to search for too.
And of course also look into all the other options that people are suggesting here.
It is not my intention to scare you off. I'm just giving you some options and things to think about. If you are talking about a small area and a few people at a time you don't need to go overboard and most of what I'm saying won't be of interest and won't apply.
Oh, one last thing .... consider a totally separate FTTC connection for your visitors, or at the very least make sure they are on a VLAN on your network that has no access to your "office/admin" network. Again it is highly unlikely to be an issue, but you don't want to make it easy for someone to get into your admin network etc etc.
No, there's one more thing too before I forget -- make sure your users can't send email without authentication on your network.