It arrived today just before lunch

Garland ,

 That's nice and a great choice. You can't do better than a tube amp and even 5 watts it real loud. I built a copy of a Fender Champ that's 6 watts. It doesn't have the choice of lower wattage settings yet if I lower the volume and the amp enough it works fine and sounds quite good I built my own cab for a Fender tweed style chassis so I used a ten " speaker yet 8" is enough that's what they came with. It doesn't have a gain either.

Garland ,

 Here's an article that explains all of this.

blog.andertons.co.uk/learn/wattage-vs-volume.

 Did you know a 100 watt tube amp is only twice as loud as a 10 watt . Then where speakers come in it's how efficient a speaker is that` determines the tone and out put of the same wattage amp. also the size will make it louder pushing more air.

 I once used a 60's fender champ 6 watt tube amp and built a cab with 2 12" speakers it not only was real loud for 6 watts it didn't break up as soon. I didn't need that much. It was a test later I rebuilt a Fender Music Master bass amp same size chassis as a fender camp and turned it into a Princeton used a larger power transformer and out put transformer the stock amp was 12 watts this change took it to 35 watts and with the same 2 12" speakers same cab I built it was so loud . I put` it back in the 1 12" cab that came with the original music master with one 12" and it is still loud and stays clean until almost cranked to 8 on the volume. It uses two power tubes which makes it a push/ pull which even the stock music master was even the same 6V6 power tubes. The amp you have is single ended which has one power tube. you can also still make a single end tube amp with 2 power tubes for twice the power they are just wired in parallel and use a different output transformer they still break up earlier because the nature of single ended amps is much different the tubes are biased to run harder more bias voltage to the tubes and they are both always working where a push pull with 2 output tubes on tube is off the other on is biased colder some have 4 output tubes yet are wired in pairs offering more watts. They are different animals than single ended.  As far as tubes yes some brands are better than others most often they are EL84 or 6V6 both are max 12 watt tubes yet some makes of either type will handle 14 watts like the Solvtec and   Electro- Harmonix made in Russia or the better ones made by JJ I use those then there are the NOS American made RCA and mullard  and others than are built to take 14 watts.   they cost a lot. For even higher power there are 6L6GC all GC means is glass tube and the wattage. They put out twice the wattage a 6V6 CG does. Some use 4 in pairs. here your into the 85 to 100 watt amps with 4 power tubes. 40 watt with 2 . 

 The tubes depend on the tone you are after. I don't know what brand are in your amp. If you are looking for a less bright high end and more bottom go with the JJ brand . They are what I use and can take a real beating one of the best that sound like to old NOS tubes. RCA Mullard ext.

 Weber makes some great speakers. you have an 8" yet each has am ohm rating on the speaker so you have to use the same rating. For a nice clean sound that is more alive and musical there are two types of magnets and cones. Ceramic magnets and ALNICO the later offers a more musical sound and for less break up of distortion use a ribbed cone rather than a smooth unribbed cone. Weber calls them their signature series the alnico sig 8 S was what I used they come in either 4 or 8 ohm . the ceramic I tried in the 8S it was ok but dry sounding not as musical. They cost more than they did when I had mine. I have a ALNICO sig 12 s  in my larger amp wish I kept the ALNICO sig 10 s I had for my champ or even on of the 8" the Ceramic speakers just don't quite cut it. There are other brands like Eminence yet they cost more for the same type. Same with Celestion which vox used and there are Jensen speakers . I found the Weber sig models to be the best bang for the buck.  here's there site.