I have 20 sets of no 4 since I first enlisted, 21 if you include a cheesy set I bought to put into my display set...
We will grow, sideways mainly, so give yourself some allowance. Make sure you can squat comfortable in them. This is not fashion, comfort is paramount. You can always tighten or adjust the buttons.
Keep one set for parades and the "smart 4"
Its expensive to buy epilets for all the sets, esp if you are a cadet and change ranks, but the cost of forgetting them is high... so decide which is more important esp if you are forgetful like me
Keep a couple sets which have all the badges sewn on them, eg IPPT, JTC, Guards, unarmed combat, jump badges etc but leave the rest blank, as they cost a lot, and sometimes we rather not look too "on" esp in a new unit or meeting regulars who may feel intimidated or even jealous.
Berets need to be seasoned, and get the right sizing and take your time. I sit on them in classes to get them to fold the right way sooner. A nice beret ensure you avoid looking like Strawberry Shortcake!
Jockey caps keep the sun out and are meant to have a lax fit, otherwise you will feel hot.
Label your clothes esp the caps as everyone has the same one.
No 3 are working clothes and should not be too tight again. Most units allow you to use your own shoes, but save the $$ and get the army ones for free (or using credits these days).
No 2 are rarely used, so just loan them, but a No 1 is used every now and then, so if you think that is the case, tailor made one. If you hit Major, they used to give you one free (not sure if this is still the case), put all your medals and badges, this one is a smart uniform! You can even use it for weddings.
PT kits during training are usualy standard issue, but later on, you can wear your own gear in many cases.
If you really want to wear a tee shirt under the uniform, get a dri fit one. But if you go outfield, its not advisable, its too hot.
I use gloves if there is a lot of training, for breaking falls, when I need to use ropes, or other field excercises, remember many plants have thorns and rocks are sharp.