Ok. I'm based in the Land of Oz, so the ratings are prolly a bit blurred. I'm prolly somewhere in 4.0-4.5. Just started playing after 6-7 years off (stopped playing at end of high school).
When I started playing again (about 2 months ago) this is what I bought and how I bought it.
Racquets - used to play with Head PC600, found it has minor cracks. Couldnt purchase any more, so I looked around and demo'd a heap of frames (very hard to find demo "player" sticks). Ended up loving the K90, so I bought 3 at wholesale through Wilson and they made sure they were 3 that were fairly close in Weight, HL and SW(my tennis centre is wilson sponsored). Also got a nice super-six wilson bag at cost.
Strings - Still fiddling round with this. Currently loving the ALU Rough, going to try these on crosses with gut in the mains for feel. When I decide on the right string, I will buy a reel, until then I buy sets and half-sets. With Tension, you need to be able to play with different tensions. Work out for the racquet you are using the high and low (+- 5lbs), and flow from there. I'm deciding what different tensions to have my 3 racquets at. Whether 2 at the one tension and one at another, or have them spaced, or all at the same tension.
Shoes - Settled on the Adidas Barricade 4's, mainly cause of support. I find myself wearing these 24/7 atm. But when I decided on them, I bought from a direct factory outlet, paying about half price.\
Apparel - bought nike and adidas. I got the good stuff because it doesnt stick to you with sweat and feels really light when they are full of sweat. I bought direct factory again, saving a ton. And only got 2 sets (2 shirts, 2 shorts, hat). I inveseted into a pair of sunnies aswell because it was a tax-deduction for me.
Balls - There is no way you can judge your game, and make adjustments with dud balls. And they go dead before they look dead. As soon as they loose a little bit of pressure, its time to add them to the pile and sell them to a kiddie coach. I find a new set of balls every 3 sets is about right (or 3 hours of solid ball-crushing hitting)
String Machine - I have one that an ex- satellite player friend gave to me, but I much prefer paying the $15AUS it costs for my club stringer to string it. He does it quicker, is on hand, and I trust him (ex Davis Cup Stringer). Can't say the same for myself. I have a family of my own and prefer spending time with them rather than stringing. However, if you are travelling, and cost-conscious then get your own portable machine. My time is worth more than $15 per hour.
Grips - Much like string, once you settle on what you like, purchase by the roll. I find myself changing grips every 1-2 weeks depending on play. If i'm playing a tournament, fresh grips and string.
Training Aids - I don't have any of these things. I hire a ball machine from time to time from my tennis centre. But the BEST thing to have is the last two points...
Coach - INVEST in a good coach. The best advice to give. Research your coach more than your racquet. I spend about 6-7 weeks looking at different coaches training before I decided on the one I use. And he is only available during the school holidays because he is booked solid. So I get 2-3 lessons every 2-3 months
Hitting Partner - Extremely important. If you cant find a hitting partner thats BETTER than you, then play more fixtures! Don't just rally! Unless you are specifically working on something and there is a purpose to it. If you find yourself mindlessly hitting rally balls, play a set! Practice as though its war, and war will become as practice!
Fitness - The best thing to focus on here is balance, footwork and flexibility. There is nothing more powerful than the combination of balance, technique and flexibility. Do what you need to do, but I have always found freeweights and bodyweight excercises more than enough. Interval Running, Skipping Ropes, Home weight bench, Tennis court. All you need.