HL Fund advice for personal savings

Hi All

(38M) married, 1 child, no debt

68k salary, financial breakdown:

350k Home semi, 48k outstanding mortgage. (5.28%)

100k Company pension

32k Company Share Scheme (matures 2029)

70k Cash

5K emergency fund in joint account (wife)

4k Instant Access ISA Monzo (3.15%)

3k Company SIP

2k junior ISA (1 year old)

1k in another instant ISA in case of earlier access as junior ISA is locked in.

The plan:

50k to pay off mortgage. Interest 5.28% balance 48k+2k early repayment fee (First Direct)

20k to put into a index fund with average risk. When I look at HL website there are so many choices?

Question 1: which Fund should I research? Even S&P has 6 options

Question 2: Should i put the lump sum of 20k in or 5k and drip feed monthly?

Thanks