dont transplant five day old plants wait a couple of weeks and they will be much easier to transplant and also dont use a 2liter bottle go buy some decent size pots 3 gallon pot would be a good size, some potting soil and some perlite to mix in.
wouldnt top if you are going to switch to flowering that soon if you wait another week before flowering you could pinch the top growth tip and then switch to flowering if you do decide to top, it is usually done either in veg or at the time of switching to flowering this gives the side branches time to grow during the stretch period of flowering.
still recomend veg nutrients, if you only buy one and not both would buy a veg nutrient and you may not ever reach full strength so just look at your plants and decide if you need to increase the strength.
bloom nutrients may help a little but the plant doesnt need that much phosphourus to flower in fact you veg nutrients and soil should have plenty and you will be less likely to have problems in flowering due to nute lockout or excessive yellowing due to insufficient nitrogen.