Okay, first about the annealing. As you already may have found, brass is worked cold (as opposed to iron, you useally work hot). When you add force to the piece it gets harder and harder. To solve this, you have to anneal the piece from time to time. This is done by adding heat (untill it starts glowing (make sure not the melt the brass!) and then cool it down again. Just do some tests with this. Most of the time I let it cool fast by dropping the piece into water. At other times I let it cool slowly by air, which gives just some different effects. Just try for yourself to get a feeling. If you don't anneal the brass can crack as it can't deformed anymore at some point.
For soldering brass I wouldn't use soldering tin. Don't know if it would work at all, but I myself use silver-solder with low melting point, as is used by yewellers. Therefore you need a soldering device which can get up to 900-1300 degrees Celsius. Just do some search on yewellery making (especially rings etc) on youtube to get more feeling about this.
About the tinning different ways to achieve that are know. Simplest (and the way I used to do it myself) is bring your work to a electrolytically tinning company, pay them some money and get your pieces back tinned. Another option is to go for some tinning paste. Several branches are on the market and others on here have had good results using those. Just do a search and you'll find some posts on that. We discussed this another time already. Another way that was mentioned by then is fire tinning. If I got it rigth you head the piece and just rub a block of tin along the piece and follow with a wet cloth. Don't have any experience with that, myself. Same method can be used to tinn a piece partially.
Also melting tin and dipping the piece to be tinned into the liquid tin is possible, and if I remember right Matt Amt has had good results with that. But it seems that method is rather difficult and need some experience to yield good results.
Hope this helps, and please, post pictures of the results