Re: Rent the backline / buy the backline ?
If there's no one in your area doing it professionally (ie: good selection, well maintained, in cases, with full support) then it might be a market to get into. However, no one is more fickle than musicians (except agents who only have a wish list from the musicians), so your pursuit of the most-likely-to-pay-for-itself inventory will never end. I'd been doing half-assed backline up until about 2 years ago when a nice local venue opened and started flying in numerous bigger acts. Since I was lucky enough not to have a serious backline source within 150 miles I got I stuff together and purchased the most popular items. It's been a good part of my business since then.
However, it can take years for some pieces to pay for themselves (and their cases), plus you'll want support cases (workboxes, etc.) to keep all the spares you'll need to take to every gig. In other words, don't buy backline on credit. It's unlikely to ever pay off.
The best guide to what you'll need in your inventory is the riders you've been given. There were also a couple of fantastic threads in the old LAB that are very informative.
Maybe you can buy your buddy some cases. Audiopile is a good source.
One good thing about most backline: Other than keyboards, if you buy the right gear it'll never be outdated. Heck, I had a Peavey Session 400 go out last weekend. First time in 4 years, but still.
