Hey JV,
Sounds like that will be a fun setup.
One thing I can recommend you try out is the Fishman Loudbox Mini amp. I was gonna get one of those marshall amps until I played on this one. I have the fishman and love it. I love the sound of it for a vocal and instrument amp. It has one balanced (mic) channel and one line channel. It’s tiny but doesn’t sound like it. I appreciate that, because as a teen I used to lug around a bi-amped bass rig to get the sound I wanted. It does have a balanced out for feeding a PA. The only downside, the mic channel does not have phantom power (condensers typically need phantom power). I picked up a cheapie ($30) tube preamp with phantom power, and that problem is solved. They have a higher power unit now ($500 range) that does have phantom power, but oddly, I don’t like the sound of the amp as well. Admittedly, I generally plug into my amp when I am using it (typically playing at churches). Micing an instrument, it sounds pretty good when I have tried it and I did play out with it as such once and I thought it sounded decent.
As far as mics, it all depends on how much money you want to spend and what your voice sounds like. As far as a simple vocal workhorse, a Shure SM58 ($100) is staple in many bands. For grass in particular, you usually see more condensers in use such as the AT 40 series ($300 and up) and 20 series as well ($100 and up). I think those might a really good bet for instruments AND vocals as those are better than many condensers for vocals (many that are great for instruments are kind of harsh for vocals). Shure SM81s (about $350) are great instrument mics. I have heard that an SM7 ($350?) is great for many vocalists, but I have not personally used one. If you want to spend more on mics, you can find plenty of opportunities. There are many mics that run into the thousands of dollars. All that said, I bought some extremely cheap condensers (MXL 990 and 991) for recording, and I was blown away by their performance. They aren’t vocal friendly, but they were about $100 for the pair and I am thrilled with them for instruments.
Sorry… that was just kind of a flood of info, but I wasn’t really sure what price range you were looking. Once you give us that info, perhaps I and others can maybe give some more specific help.