Using permanent it semi permanent I think the possibility of your grey hair ending up orange is very high - not a statistician but I'd say 95% (voice of experience).
It will not blend in with the rest of your hair. You will have a ring of orange round your head.
Get a deal conditioning mask
It doesn't really matter which you get. They are usually in a tub. slather it on, paying particular emphasis to your ends.
Leave for 15 minutes past whatever time is on the tub.
Comb through starting at the end of your hair (furthest from your roots.)
Wash out.
Shampoo hair, condition it with normal conditioner, comb through, rinse, dab your hair dryish with a towel (don't rub it). Comb through again.
Blow dry or leave to air dry. If you blow dry use a downward method - so you are smoothing the cuticles down.
After so much conditioner your hair may feel greasy. Just wash it again - the next day or if you can't bear it later that day.
Next time you wash your hair put conditioner on the ends rather than the whole way up to your roots.
Does it look like you've got split ends? If you have plait your hair and trim off the bits that stick out of the sides.
If you want to cut your hair I'd do it damp.Get a pair of proper hair dressings scissors and look at a few you tube videos. Only trim a small amount 1/2" / couple of cm. When the hair drys it will shrink up a bit.
Don't tackle your fringe unless you are feeling super confident.
You can if you want rather than cutting across cut up, or I've eve tackled my fringe with a safety razor to thin it out (risky)
On holiday you can buy spray in conditioner/after swim stuff
Get some scrunchies and tie your hair up.
And to reiterate don't dye it . If you make a hash of it it it will make you feel loads worse.