An individual can fund an IFISA however they wish to before the 5th April in that tax year to make use of that tax year’s allowance. They can invest a lump sum or spread the funding over the year, however they see fit.
PLEASE REMEMBER, REGARDLESS OF THE TAX BENEFITS, CAPITAL IS AT RISK
Whether investments are held within a IFISA or in a general account, they are not covered by the FSCS; the government backed deposit insurance scheme that protects bank deposits including Cash ISAs. The tax benefits available in an IFISA are subject to status and your capital is at risk. The tax benefits of an IFISA are also subject to change by the government.