i ride a mans bike and wear skirts and never found it an issue, always have, just tip it to the side slightly to get on!
we have the four boys and then dd, we bought an orange balance bike, just because it was bright and cheerful! ds4 uses it at the moment but dd will as well.
the boys have the micro scooter, the big ones and we have on thats black bought purely because is was on sale at £39!! bargain when they are meant to be £95! and the other is the black and green one, chosen because at school there are load of the purple ones etc and i didnt want it getting muddled up! ds3 who is 7 had a purple fairy scooter until very recently it was 'tinkerbell and friends' he got lots of fairy toys for xmas and loves pink and purple and all things sparkly.
i do get dd nice girly clothes, skirts, dresses etc, but not in pink as i dont like it as a colour and it doesnt suit her colouring, she has greens, blues, dark purples, red etc. i do have a lovely coat from pumpkin patch which was from their 'boy' range but dd will wear it next winter as its warm and nice, she also has a snowsuit from jojomamambebe which is blue with flowers a sort of cath kidston print. she also wears the boys old dungarees and cord trousers.
i think if a bike is just handed down then it makes sense to buy unisex, we have black and silver and orange bikes and they will all be passed down, if a child asks for one for xmas and bdays then they would get some input but ultimately it will come down to the best quality bike we can get for a good price and i would rule out character bikes on that basis as they are shite! mine have dawes, scott bikes etc decent quality and they tend to be unisex for younger children. i would repaint a back or buy accessories for any child tho, i remember i had a bike that was red and was to be handed down to my younger sister, she wanted it yellow and i remember my dad spray painting it in the kitchen it had big silver mudguards and a silver bell, so still unisex but in the colour my sister wanted.
i also remember my mum buying me a new bike and HATING the fact it was a purple raleigh bianca! i wanted a red bmx! as soon as i could i got a paper round and saved up bought myself a bike of my choice!