A1.
CSV export character set handling nothing change from eguide 2.54 to 2.6.
So I have no more suggestion from before comment.

A2.
Excel export template makes very limited.
You need change template for up to limit value.
For example eguide_reception.html change:
@@ -96,9 +96,9 @@
 </form>
 <p align='right'>
 [
  <a href="receipt.php?op=csv&amp;eid=<{$eid}><{if $exid}>&amp;sub=<{$exid}><{/if}>"><{$smarty.const._MD_CSV_OUT}></a>
- | <a href="export.php?eid=<{$eid}><{if $exid}>&amp;sub=<{$exid}><{/if}>"><{$smarty.const._MD_EXPORT_OUT}></a>
+ | <a href="export.php?eid=<{$eid}><{if $exid}>&amp;sub=<{$exid}><{/if}>&amp;line=200"><{$smarty.const._MD_EXPORT_OUT}></a>
  | <a href="sendinfo.php?eid=<{$eid}><{if $exid}>&amp;sub=<{$exid}><{/if}>"><{$smarty.const._MD_INFO_MAIL}></a>
 ] 
 <a href="receipt.php?op=print&amp;eid=<{$eid}><{if $exid}>&amp;sub=<{$exid}><{/if}>"><img src="images/printer.png" alt="<{$smarty.const._PRINT}>" border="0" /></a>
 </p>