Hi SydneyFox and thanks for joining us

Re: your questions:
1) The "FXT timeframe" selection allows you to select which time-frames you are going to test with. That is, this corresponds to the "Timeframe" selection that you choose in the MT4 Strategy Tester. If you typically test only in the M5 time-frame, select only this option. This is primarily a disk-saving measure, so if you have plenty of disk space, you can leave all time-frames checked.
2) This depends on the symbol - obviously the more active trading the symbol is (eg. EURUSD is very active), then the more data. Roughly speaking, each symbol will take around several hundred megabytes per FXT file.
3) For a newbie, the best bet is to select the new server in Tickstory and re-do your export. For the more advanced user, you can move your HST files to the new server location. ou can also edit FXT information if necessary.
Don't forget that there's plenty more information in the user manual which you can access by pressing F1 in the application.
Happy back-testing!