I've worshiped with Plymouth Brethren my whole life. Here's a few quick bits of info:
1. We don't usually refer to ourselves as Plymouth Brethren because having a name denotes a denomination, and we are not in favor of schisms in the body of Christ. However, we do understand the desire to know what people believe and that denominations help provide that information, so it's not a contentious issue for us.
2. Unfortunately, there are schisms even in the Plymouth Brethren, which started quite early in its existence and which led to the division of open and exclusive assemblies. We tend to call our groups assemblies and our gatherings meetings (and sometimes we call our groups meetings as well), to avoid the misnomer of "going to church." Exclusive assemblies will allow visitors to attend the worship meeting but not participate until accepted into fellowship; open assemblies will allow visitors to participate, usually after speaking briefly with an elder or two. The exclusive assemblies usually call their buildings gospel halls, and the open assemblies usually call their buildings chapels or Bible chapels.
3. You're right that our theology is pretty mainstream fundamental, but here are the three main differences in practice:
a. we don't have pastors; we have a plurality of elders and the brothers who have a gift of teaching (esp the elders) share the responsibility of teaching
b. our worship service is an entire meeting focused on remembering the Lord Jesus Christ, in His death and resurrection as well as the perfections and beauties of His character and work; as the Spirit leads, the brothers share from the Scriptures in that regard, lead in prayer, and call out hymns focused on Christ, and then we share the cup and the bread; this is done every week, usually the first meeting on Sunday morning, then we have a short break followed by the teaching meeting for adults and Sunday School for children (oh, one other distinctive about the worship meeting, aka the Lord's Supper, is usually there are no instruments - the singing is a capela, and you might not be familiar with the hymns)
c. in obedience to I Corinthians 11, the women wear head coverings of some type; exclusive assemblies tend to wear hats, and open assemblies tend to wear lace coverings similar to what Catholics used to wear; it's fine for visitors to an open meeting to not wear a head covering, but exclusive meetings may ask visitors to do so and provide one if needed
4. I found your post because I was looking for the online directory of North American assemblies...it used to be under assemblydirectory.org, but it no longer is, and I can't find it anywhere else I've looked. I'll have to ask around and see if anyone knows where it's located now, and if I'm successful, I'll let you know the web address.
PS - this didn't end up being very quick, did it?

I hope it's not information overload; if you have any questions, I'd be happy to try to answer them