Glad to hear you want to have a go,but be warned its very addictive and you may find yourself staring over fences at sheep you've never even noticed were there before. I got started just as your doing and yes its intimadating, so many questions,so many choices, lets see if I can help.
Q1 Your home made drop spindle should be just as good as any bought one, never diss DH, just give him a little more information.The making of a good drop spindle is easy if you know how it works, everything depends on the distance from the botom of the shaft to the whorl(the round disc).When you can be there as DH makes yours you can decide whats best for you.When he puts the whorl on make it a tight fit and put it right at the end of shaft,then try spining it on a good long leader thread and count how long it goes for, then move the whorl up a little and try again, keep moving and trying untill you find the best position.Obviously light weight materials are best this is why although they are prettier the spindles turned on a lathe out of one piece of wood are not always the best to spin with.My DH has got so good at it he makes spindles for sale at my Spinners and Weavers Guild,and craft fairs.
Q2 Everything comes with practice, with well prepard fibre I can now spin lace weight.
Q3 Not easily, its easier to adapt a pattern than adapt a yarn.
Q4 I believe there is a machine washable merino available(its treated in some way) but usually a pure wool garment home made or bought is best hand wash only.
Q5 the only way to tell for sure is to get your hands on it, but most places will give item descriptions and main uses. The softer the fibre the more likely it is to felt, the coarser the less feltable, the trick is hitting a happy balance.
Q6 Roving already has a slight twist, so to make it draftable(easy to pull apart) you need to spin it in the other direction.In tops the fibers lie straight, for a beginner I would reccomend tops, less chance of going wrong.
Q7 If you spin 2ozs of (processed) fibre, you get 2ozs of yarn. Its yardage depends on how thick or thin its spun.
Hope this helps.