Query Chatter Feed, Topics, and Groups

First off, my end goal is lofty and time-consuming, but we need metrics and this is the best way to do it (that I can think of). Originally, a chatter post was created on the quote, case, or where making a request and the end user marked it with a topic. An answer would be given and then done. Now, we've moved to a group. So my question: What is the best/most efficient way to query FeedItem, FeedComment, Topic, and CollaborationGroup? I would like to see all posts with a certain topic and their comments. Then I'd like to see all posts from the group with their comments. I'll then use the createddate to gather metrics. I've been able to do individual queries in the developer console, but I'd like to send these all to a .csv (I have the apex code to do that) and possibly insert into a local SQL db. I just can't find the relationships between feeditem and topic, feedcomment and topic. Here are my queries so far:

ChatterActivity0caselect Id, CommentCount, CommentReceivedCount, InfluenceRawRank, LikeReceivedCount, ParentId, PostCount from ChatterActivity limit 100FeedComment0D7SELECT Id, CommentBody, CreatedDate, CreatedById, FeedItemId, ParentId FROM FeedCommentFeedItem0D5select Id, Body, CommentCount, CreatedDate, LikeCount, LinkUrl, ParentId, RelatedRecordId, Title, Type from FeedItem WHERE Type = 'TextPost'Topic0TOselect Id, Name, CreatedById, CreatedDate, Description, SystemModstamp from TopicCollaborationGroup0F9select Id, Name, Description, InformationBody, InformationTitle from CollaborationGroupCollaborationGroupFeed0D5select Id, Body, CommentCount, CreatedById, CreatedDate, LikeCount, LinkUrl, ParentId, RelatedRecordId, Title, Type from CollaborationGroupFeed

Update: TopicAssignment Query

select id, topicid, entityid, entitykeyprefix, entitytype, createddate, createdbyid from TopicAssignment

Update: My Solution

Here is the beginning framework for my solution, and how to get it to display in debug. Obviously record count will get too high, but that's the nth step down the road.

List<FeedItem> chatFeed = [SELECT  Id, Body, CommentCount, CreatedDate, LikeCount, LinkUrl, ParentId, RelatedRecordId, Title, Type,    (SELECT Id, CommentBody, CreatedDate, CreatedById, FeedItemId, ParentId FROM FeedComments)FROM FeedItem WHERE Id IN (    SELECT EntityId FROM TopicAssignment    WHERE EntityType = 'FeedItem'    AND TopicId = '<TOPIC_ID_HERE>') LIMIT 100];For(FeedItem fi : chatFeed) {    System.debug(fi);    For (FeedComment fc : fi.FeedComments) {        System.debug(fc);    }}