Greetings, Alavecchia, and welcome. You wrote:

<<I made my first Roth IRA Contribution in tax year 1999. Now I want to make another 2000 contribution, but I would like to do this with a different broker. Does anyone know how having my Roth in two separate accounts will affect me, if at all? Specifically, how will it impact my vesting towards the five years needed before a withdrawal for a first home?>>

You may open as many Roth IRAs to receive your annual contributions as you wish without impact. For withdrawal purposes, the five-year limit begins with your original annual contribution to the first IRA. Annual contributions to different accounts after that do NOT start a new 5-year period.

Regards..Pixy