firstly, do you intend to let your child sleep in the baby cot long term?
or will your child end up sleeping with you instead?
for my girl, my aunt bought her a babycot, cos about 500 plus.
end up only used during the first month then wasted.
if you are intending to let your child sleep in the cot long term, then of cos, it is worth investing in a BABYSAFE mattress.
pricewise, of cos will be more expensive but the usage is diff, its SAFE.
this answers qn 1 & 2.
qn4 & 5,
baby is so young, dont require pillow and bolster the first few mths, maybe up to a year old (depending on what your child likes, to hug or not hug anything to sleep).
pillow and bolster put beside baby is fine, as long doesnt cover baby's face.
baby doesnt need to sleep on a pillow yet, so not a requirement to get a baby safe pillow.
weather so warm, just a normal towel or blankie is good enuf to cover baby (til mid chest only)
blanket big, can fold or just dont cover baby fully.
blankie or comforter, up to you, but comforter is thicker right? if sleeping in air con room maybe can use that.
if just using fan, blankie is good enuf, cos the weather is warm lately.
for changing mat, actually to me, not really a need to.
i did buy, end up lazy to use cos need to take in and out.
if you change diaper fast enuf, shld be ok.
but you can buy a cheap one to use for the first few mths cos baby tend to pee alot, just in case you changing half way she pee/poo.
unless baby wearing nappies, wud be good to have a changing mat underneath if not when leak, you end up changing bedsheets more.
as for qn3, you may want to shop arnd at diff dept stores to compare prices, but i believe more or less they are almost the same price.
hope this helps.