Here are some answers to clear up your questions.
First, you shouldn't have to settle for your test being in the 300ng range when it should be between 600-900. Unless you are an older male (50+) with the potential for prostate problems/prostate cancer you should be able to safely have your levels brought up.
Don't know much about the Androgel products, but my doc says the injections are better. As mentioned, more bang for your buck. Now if your a needle phobic type stop worrying. The injections themselves don't hurt. The needle is usually 1-1/2" long at most. I even had a shot with a 5/8" long needle, it just takes longer to inject the testosterone when the needle is a smaller gauge. You doc can also use Gebauers Ethyl-Chloride while he is giving the injection. it is a topical skin refrigerant/anesthetic that numbs the pain associated with injections. With this you won't feel the injection at all. After you get the injection there is a barely noticable burning sensation from the benzyl alcohol that is in the injection. The burning fades in an hour or so.
Arimidex (Anastrozole) is technically a breast cancer drug usually given to women to combat estrogen dependant breast cancer. Basically it lowers estrogen. In men, it's used when taking steroids/testosterone in order to prevent side effects from excess estrogen that aromatizes from the exogeneous testosterone your taking. So in a nutshell it prevents you from growing a nice set of tits and also combats water retention/bloating. Arimidex can, on it's own raise testosterone levels. By lowering your estrogen your body will make more testosterone so that it can aromitize some of it into estrogen. However since the Arimidex inhibits the aromitase enzyme, the extra testosterone your body puts out won't convert to estrogen, hence a higher testosterone level. Just be careful because Arimidex is very strong and you can lower your estrogen too much which will result in sore joints and some other undesirable side effects. Arimidex will also prevent your testicles from completely shutting down from the test therapy, although the usual test dose is about 100mg a week, so shutdown isn't really a big issue like it is with 300mg a week and up like some of the hardcore steroid users take.
In keeping with the whole anti estrogen thing, you may want to look into a product called Myomin. It's made by a company called Chi's Enterprise. It is an aromatase inhibitor usually used for women to reduce estrogen in order to shrink fibroids. It is actually very effective. I use this in conjunction with the Arimidex. just so you are aware you'll need a script from the doc for Arimidex and it costs about $135 for 15 pills. Good Luck getting insurance to cover it too. Myomin you can get from the Chi website,or other health food /nutraceutical suppliers. I'm thinking of stacking Myomin with Biotest's "M" and Alpha Male once my initial round of HRT is done. This may be a great stack of product to keep test high and estrogen low.
Hope this answers some of the questions in this thread. I'm by no means an expert, but I know enough to get by. You should all check out the Steroid forum her at T-Nation, there are probably a handful of very knowledgable guys there that can answer everything you could possibly want to know about this stuff.