Base used in Claisen Condensation Here's what I read about which base to use in Claisen Condensation reaction (two esters or ester + carbonyl compound forming a beta keto-ester or beta-diketone): 


  The base used must not interfere with the reaction by
  undergoing nucleophilic substitution or addition with a carbonyl
  carbon. For this reason, the conjugate sodium alkoxide base of the
  alcohol formed (e.g. sodium ethoxide if ethanol is formed) is often
  used, since the alkoxide is regenerated. In mixed Claisen
  condensations, a non-nucleophilic base such as lithium
  diisopropylamide, or LDA, may be used, since only one compound is
  enolizable. LDA is not commonly used in the classic Claisen
  or Dieckmann condensations due to enolization of
  the electrophilic ester.


Here's what I didn't understand, particularly -


Why is the conjugate sodium alkoxide base of alcohol generated, used? The paragraph talks about regeneration of alkoxide ion; but I didn't really understand that part. (Seems like something related to chemical equilibrium?)
They said that Lithium Diisopropylamide is NOT generally used due to enolisation of electrophilic ester. What do they mean by it? Why can't we use LDA? Which bases can we use instead?


Could someone please answer the above two questions, with proper explanation? Thanks a lot!
Consider that there may be other reactions also going on, not just acid-base chemistry. So, for instance in the Claisen reaction of ethyl acetate, if methoxide was used instead of ethoxide then you may get methyl acetate formed as well.