Reincarnate Help?

[Gwazi Magnum]

Some things I bit confused on with the spell.

Do you keep anything from the old race other than mental ability scores?
Like for example skill bonuses, humans bonus skill points or feats etc?

For the new race do I still need to take their HD and LA?

Also would it be possible to reincarnate into a Warforged body?

[Feralventas]

If you go by the spell itself, 99/100 times there is a specific creature that you would become.

You retain No part of the racial stats you were before, including the removal of Level Adjustments, Racial HD, stat boosts and supernatural, spell-like, or extraordinary abilities.

If you hit DM choice or otherwise are allowed to pick and choose your own results, then yes, you would add whatever Level Adjustments, Racial HD, stat boosts and supernatural, spell like, or extraordinary abilities instead.

So if you went from ELF to Phrenic(template) Halfling,
you would lose the elf's Low Light Vision, trans/meditative sleep replacement, conditional save bonus vs certain things, and the +2 to dex and -2 to Constitution would be gone.

You instead get the Halfling's racial traits (small size bonuses/penalties, +2 dex, -2 strength, etc etc, and the effects of the template which include more stat-boosts and Psi-like abilities, with a +3 level adjustment for the template.